The Terms and Conditions on all the Bitrefill pages for purchasing Amazon card states the following:
Please note that if a customer redeems excessive amounts of Amazon gift cards in a short amount of time, or attempts shipping or purchasing from across country borders, Amazon may flag your account and lock your Amazon balance. Bitrefill has limited ability to assist when Amazon flags an account and is unable to request or provide refunds in these situations.
A quick internet search suggests that people have frequently have their Amazon account locked because of using gift cards, even legitimate ones, from different regions/countries or because of trying to purchase or ship goods to different countries/regions. Does this apply to you OP? Do you regularly use a VPN or Tor which would have made Amazon think you were ordering from a different country?
On another note, the Amazon Gift Card Restrictions page here (
https://www.amazon.com/gp/help/customer/display.html?nodeId=201138990), states that is it forbidden to "Purchase a gift card from an unauthorized third party as we cannot guarantee that they are legitimate." Is Bitrefill an authorized or unauthorized third party?