TRANSACTION DISPUTE

In December I paid for groceries from PNP Online using my Discover card. An amount was deducted from my account after placing the order. Upon receiving the groceries half was not on the list because there was no stock, they Reserved funds for the groceries deducted what was delivered - so where is there balance that was deducted. I contacted Discovery 5 times - emailed at least 5 to 6 times - I supp**** a letter from Pick and Pay showing them they need to release the difference - Discovery doesn't seem to want to help and worst of all coming up with one story after another they keep asking for Proof pf payment - every email to them have everything attached. This is such terrible service - I don't know what other else Discovery needs in order to pay my money back - they have proof, yet they are refusing.