Unauthorized hold of money for 7 months

When I went to an Indian restaurant their credit card machine didn't work and I've paid in cash for my dinner. FNB is still holding the money from the attempted swipe - trying to double charge - on my bank account for 7 months now. I've been told to submit a chargeback request, but I have no proof of cash payment anymore. How pathetic is this FNB? I did not authorize you to hold the amount for 7 months!