I had a student who was hopeless with numbers after being bullied at school.
S/he had a hospital job where dosages of drugs to kids were critical. S/he sat up for nights and nights with spouse and made up quick reference cards so no calcs had to be made at work - just read of drug. height/weight etc and find doseage.
Actually got a merit award for the work!
So there are always ways round problems.
If the worst, try microlights. No balance calcs needed, just weight. And if you cannot punch in empty weight, fuel weight, passenger and pilot weight into a calculator and check it is less than Max All-Up Mass, then there is truly little hope. (you don't need to calculate any of that in the exams, just before flights and in flight planning. Heck, if you know your instructor's weight and your own, and the aircraft weight, you can make a table up for different fuel loads. Oh! microlight aircraft usually have that table on display as part of the regs. helps that the regulators think microlight pilots stupid!!)
For nav, you can use Flylight's map board. Then all you have to do is be able to read the scale on a ruler. Not too hard - and can be used in the nav exam. Unlike GPS and web based calcs which everyone actually uses once qualified!
So, even if you don't leanr to fly a microlight, you'll find lost of input there to show your instructor an alternative way of doing things. And if they don't like it, find a better instructor.