Still no release of holding deposit

I returned a hired car over the weekend of 3-5th May and the holding deposit was around R5,500 because of a surcharge for the weekend. The car was returned in perfect condition. They still have not returned my deposit, 17 days later. When I enquired, they said, "Was it a cheque card?" It was, but what difference does it make? They said to phone customer services who would phone the bank to release the holding deposit. Two business days (that was two days ago). Today it was still not released, they said it will be escalated. Between them and the bank they can't get their ducks in a row. How can you return a car and 17 days later they still hold your money??