In any kind of persuasive writing like this I would focus on facts and outcomes. The formula is generally linking cause and effect back to the previous prescriptions you had. You don't want to use "weasel words" or suggest that you feel the previous prescribed amount was more effective. You want to assert that it was and this downgrade has risks to your health, pointing out the causal relationships between what the medicine does for you and its absence aggravating another condition.
So for example,
My previous rx was 1/day of $medication for migraine prevention. This regimen worked to prevent migraines which cause me $xyz and aggravate my $abc.
Same goes for the soap. You link to your surgical wounds and the risk of infection if you can't adequately bathe as a factual cause-effect chain and need.
I would leave the emotive parts out. If you have a back-and-forth correspondence with the GP and have exhausted the evidence-based reason these cuts are detrimental to your health then you can use an emotional appeal. I would also leave out the pharmacist and avoid acknowledging the cost. The cost is the argumentative lever they are using to degrade your supplies and you don't want to give it any merit in your appeal.
Feel free to post a draft here or dm, and I can offer more concrete feedback.