How long do customers get to claim non reciept of item?

Hi all

How long do customers get to claim a non reciept of item nowadays?

Just had one from 28th of March claiming they only just realised they hadn’t received it. Delivery confirmation says it was delivered on 1st of April (Not tracked I know as it was only a cheap book).

Is it worth fighting or will Amazon just find in their favour even after all this time?

Thanks in advance.