In my religious background, there is huge emphasis on fearing God, fearing His wrath, and hell. Hell is very graphical. Here are some verses showing how graphical it is:
"And if ye do it not - and ye can never do it - then guard yourselves against the Fire prepared for disbelievers, whose fuel is of men and stones." (Q 2:24) "Lo! Those who disbelieve Our revelations, We shall expose them to the Fire. As often as their skins are consumed We shall exchange them for fresh skins that they may taste the torment. Lo! Allah is ever Mighty, Wise." (Q 4:56) "For such, their habitation will be hell, and they will find no refuge therefrom" (Q 4:121) "Lo! the hypocrites (will be) in the lowest deep of the Fire, and thou wilt find no helper for them;" (Q 4:145) "Lo! those who disbelieve and deal in wrong, Allah will never forgive them, neither will He guide them unto a road, Except the road of hell, wherein they will abide for ever. And that is ever easy for Allah." (Q 4:168-169) "They will wish to come forth from the Fire, but they will not come forth from it. Theirs will be a lasting doom." (Q 5:37) "Theirs will be a bed of hell, and over them coverings (of hell). Thus do We requite wrong-doers." (Q 7:41) "O ye who believe! Lo! many of the (Jewish) rabbis and the (Christian) monks devour the wealth of mankind wantonly and debar (men) from the way of Allah. They who hoard up gold and silver and spend it not in the way of Allah, unto them give tidings (O Muhammad) of a painful doom, On the day when it will (all) be heated in the fire of hell, and their foreheads and their flanks and their backs will be branded therewith (and it will be said unto them): Here is that which ye hoarded for yourselves. Now taste of what ye used to hoard." (Q 9:35) "Know they not that whoso opposeth Allah and His messenger, his verily is fire of hell, to abide therein ? That is the extreme abasement." (Q 9:63) "Hell is before him, and he is made to drink a festering water, Which he sippeth but can hardly swallow, and death cometh unto him from every side while yet he cannot die, and before him is a harsh doom." (Q 14:16-17)
Even though I have left this religion but I get this nightmare that I am getting punishment for leaving the religion. I feel scared that what if I am wrong and end up burning in hellfire.
How to get rid of this fear so that I can live my life freely?
A lot of commenters are saying something like "if you don't believe then you have nothing to fear" and are entirely missing the point that it has been engrained into you and isn't a simple matter of intellectual belief.
The person I quoted is overstating it the intentionality of people but more importantly: I think emphasising this is counter productive. It's likely to replace your fear with bitterness. I think you will have more success if you can forgive them for doing this to you. They were well meaning but misguided and you are doing something brave by breaking the cycle. Practising the religion doesn't actually remove the fears, but by leaving the religion you'll be helping to stop this trauma from being propagated. You probably do have to recognise the harm that the commenter talks about before you can forgive the people that did it.
Forgiveness is probably better for you long term, but will take more work.
I will not forgive them for the way they try to suppress my questions. Even from my initial questioning, everyone treated me like an outcast just cuz I left their interpretation of religion. Some days ago, my dad said that too much knowledge is bad and we should not be too knowledgeable. The misogynist, hyper-conservative, toxic parents they are. If I could do, I will piss on their graves. And for imams, they think they are hooligans. I have seen from my own eyes the terrorist organization recruiting for Jihad and how mosque welcome them. Another mosque's Imam think that if you follow his interpretation, it does not matter how much you sin. You are not blasphemer. If you leave their sect, you are blasphemer. They are the source of making people radical, committing pdfilia and trying to take place of what Catholic popes used to be before Protestant Reformation. I will not forgive anyone. I may not go as far as some people like Stalin went to suppress religion but the way they lied with me, tried to suppress me and my ego, trying to make me feel that I am mentally ill just because I feel attraction to boys too or that I don't wanna marry, they don't deserve forgiveness.
It seems like your parents are behaving the way your society has taught them to behave. I imagine they were subjected to similar forms of indoctrination as you were, but yeah maybe they crossed a line in their treatment of you it was just my two cents.