FedEx asking us to pay on a link when they fail to access your payment you have to pay again using an account number. WTH

On my last month order from Shein, FedEdx was excellent, their service was on point, they asked me to pay customs using an account number at Std bank then email the POP everything went well because i had proof of payment . This time around they sent me a link to pay for customs of which i did paying using their own link. After the payment went through there was no receipt, i waited hoping that i will receive it on the email but nothing. Two days after that i received an email asking for proof of payment to be emailed to a certain email and they gave me account number citing that they have difficulties to access proof of payment when funds were paid using their link. The problem with this is that the only proof of payment i have is on the transactions i made and i dont know why they sent us links that are no user friendly. This is embarassing for a big company like them. Now i have screen shoot proof of payment from my transcation history and still waiting to hear from them, I real do not need this headache