You don't need to have an adress in The USA. To give you an example: I live in France and there is amazon.fr.
Yet I sometimes buy on amazon.de and use my french adress...
Bingo. Here was your mistake. Adding 4,000$ to a brand new acount on Amazon. It's a well know flag to see Amazon locking your account.
Bitrefill, for exemple, display a message to avoid adding a huge amount.
I know in such case Amazon asks for document much more than the police. I've been in the same situation during 9 months, and finally got my account back by playing the idiot village card
Does this site require kyc on more expensive purchases, or is it no kyc across the board?
It has been years since I used the website but if I remember correctly there is no KYC verification for "Shoppers" but only for "Earners"