Credit card disputes

I swiped my card for a preauthorised payment- which was supposed to be cancelled a few days later. I received the SMS stating the amount that was debited and recieved proof of payment and proof of cancellation from the merchant aswell. The payment was cancelled today and only a portion of the amount I swiped for was credited to me. I called into the fnb call centre who offered to send me a statement- showing a lesser amount than what I swiped for. How does this make sense. When I have the proof of payment, which is different to my statement! Truelly dissapointed in this service! <br> <br>