OK, so I just tried to look up my Prime account number. All I can find, pretty hidden, is an order number, which changes with every prolongation. Legally, I have one contract, that prolongs every year if I do not cancel. This contract has no ID (it is my email address, sort of). So if I enter the Prime order number in the new cancellation form, would I cancel the entire contract or just the running instance?

My parents wouldn't know what to fill in the contract identification field of the cancellation form.

Plenty of room for dark patterns.