Credit decreased do to their error

We opened the total sports account in January ..then set up eft for payment as we pay all our accounts that way. ..made the payment and so did we the following month..only to receive an account that we did not pay ...my fiance phned to rectify the problem was told to email his proof of payment...after several phnes calls emails and bank trips over time period of three months..fighting to prove we did pay and it was not our fault they cleared our name..ever since then weve paid in store..however they dropped our credit limit from R12 000 to R4000 and put a block on credit increase for us...we need to buy our wedding rings and cannot do so ..again my fiance been phning out so much airtime that thiz can be fixed as it was not our fault how can they penalise us for their fault..now they telling us nothing they can do and refusing to increase our credit limit..this is rediculous never ever had problems with any of our other accounts..worse service ever!! NOW THE PROBLEM STILL NOT FIXED AND WE CANNOT PURCHASE OUR RINGS!!! Im livid as saw the perfect ring on special just till the 24 th December and will now loose the perfect ring due to their incompitence