Refund

In the month of November I rented a car till end of December and further extended it from December till January.The car rental deducted money from my account for both of my rental days,the further deducted R8500 from my account which I fail to understand what is it for and now am struggling when they have to refund my money,even today in the morning I have send them an email but they refused and the lady is so rude.I have been asking them to refund me my R8500 but. Am struggling because they deducted it while they took their rental fees on the money they hold. Last week I received a call again that I still have outstanding balance of November-December payments but how did they extend my contract for while they didn't take their money.For all I know is that they have bad attirude towards this matter because I want my R8500 to be refunded in my account.