Need Advice Buying Amazon Gift Cards

[TraderCal11]

I want to use Vanilla Visa gift cards to purchase amazon gift cards from Amazon.com. I used to be able to do this within minutes, but lately any account I use Amazon takes up to 4 hours to process it. I've tried using different accounts, using accounts with a larger purchasing history, using VPN, pretty much everything. Has anybody ran into the same problem and how did they fix it? Amazon blames it on the bank, says that any transaction will take this long, but I have been doing this for months with no problems. The only other thing I can think of is the zip code? THough i never had a problem with it before. Any advice from people that have experienced similar problems would be helpful. Thanks!