Bayport consolidated my accounts and this company was also part of the consolidation

Bayport consolidated my accounts and this company was also part of the consolidation. I discovered that they provided a huge amount of money to be paid which Bayport paid into their account. Now they are refusing to refund even though they admitted that they noticed that the amount was not the amount that was supposed to be paid. They were paid extra R18000 which was supposed to be refunded but they are coming with all sorts of stories. Please help me