Wesbank private finance are pathetic

I bought a vehicle threw private finance. Did everything that the guy ask for then he said everything is done i must get insurance for him and sign documents. After everything was done he said he can't go on with the deal as the seller cant give him bank statement of the money paid from his account. So i phoned the previous owner where the seller bought the vehicle she explained that they made a deal where she bought his car and the rest of the money was paid cash. She have the agreement letter with here and was prepared to go make a affidavit off the purchased agreement and still they said they don't allow it. I paid 2k for the inspection test and already paid prorata on my insurance who will be responsible for that now