Proxy = Vpn
It is my way of thinking, now VPNs are as detectable as Proxy and they act almost in the same way, if you want you can try with another browser, make the purchase among others, Eliminate all possible factors, Amazon is Amazon, you will spend example 5 Thousand Dollars they generate a lot daily, detecting you is not difficult, they get used to it, if said payment comes from an unsuitable source at your own risk but well, I will not say more. 