Aweful and a waste of time

So I have a Fevertree revolving account, never missed a payment and not in arrears, I have over R3000 available, according to the statement and I phoned them this morning and asked if I could get glasses from Specsaversfor my wife. It's a revolving credit account so why do they want me to go through the whole credit application process again. It's a principle thing for me, it's a revolving credit account so why this again. I have had one or two problems in the last six months but Fevertree has always been a priority of mine to pay. I have 5 months left to pay and never again and will not be referring them to anyone. Personally I think it's disgusting.