Is it permissible to purchase non-medicinal goods (such as diapers and perfumes) using a medical prescription, in order to utilize an unspent health insurance amount, given that this amount will be forfeited at the start of the new year, and that the fund deducts a monthly fee for its services?

If you participated in a forbidden commercial insurance with an annual premium and you fear the year will end before you can benefit from what you paid for, and you cannot claim your right openly, then you are permitted to benefit from your right which you paid for in the manner mentioned, but you are not permitted to take more than that. Ibn al-Qayyim stated that lying is permissible to attain a right if it does not involve harm to others.