Dishonestly and destroying my credit history

I called finchoice on the 25 March to make a deposit payment arrangements,I agreed with them to pay a mobi ACC and monthly ACC both at once,they will allocate the money to respective accounts.then they decided to pay all the money to 1 account and leave the other,now the other account is in arrears and they keep adding interest everyday,instead of having a balance of R1027.00.i have to pay R2600.00.and no one bothers to call me,even after about 10 emails .so I'm basically gonna be blacklisted because their agents didn't do their job.