Discovery refuses to close paid up credit card

I am in the process of purchasing a property and one of the requirements is that I should close all unused lines of credit. I then proceeded to close my unused (paid up) Discovery Card but the card division has not been useful at all. After multiple calls with Discovery, they kept telling me that the account will be closed in 48 hours... it has now been 192 hours and counting.

Discovery please assist, we urgently need this account closed.