Credit card

I ve got credit card with standard bank .they gave R27.500.I got it I think 2013 I never used that year . To my surprise they say I owe them almost 20.000. The money that I can say I owe them 7000 . I never ever use that amount is to much , I got lot of notification from credit that say my balance is 20.000 n now I can't withdraw my money they have blocked me , n I don't get their statement I wanna know what went wrong with this people hence I say I got their notification from them on the 01 October 2015 still people please help :I'd ***, ***