Woolworths credit card

I have a credit card with Woolworths they gave me 1100 at first then after paying my 1st instalment which was R80.00 they then added another R1100 now my instalment went to R1460 which does not make sense and i believe that they were supposed to communicate with me and advice that if i use the other R1100 then my instalment will be R1460 if the extra R1100 was given to me by mistake then it not my fault i cannot afford R1460 and now it impacting my credit score please assist