Denied to use my American Express card

Hi I was denied to you my American Express card at one of you bp fuel station, I have received an email that I can start using my nedbank American Express card in any bp garage. Last night I wanted to purchase the cashier said no harshly, I told her I got an email she Insisted “no” I then asked her to check if it will go through she kept on saying no.

Which didn’t make sense because in the other branches it works.

I reported it on bp customer complaints but I haven’t gotten any responses.