well then you need to pay by PayMate.

PayPal is only one of the three safe payment methods that a seller has to offer.

They don't have to accpet paypal, they can choose any of the three they like.

So, what is written in the listing? Do they say they take PayPal? if they do, then you have a course of action, but if they say they only take PayMate, then that's what you agreed to.