Three months & still no deposit refunded

The antics Enterprise car rentals have brought on are unbelievable. Firstly, charged my account 49 pound for excessive damage to vehicle which was a scratch five inches long. After a reviewer they re-embursed my account the 49 pound.
Then claimed that the vehicle was returned a day late. This also was a lie as it was returned 30 minutes early.
I took out extra insurance to reduce my excess from 1000 pound to 100 pound and paid a deposit of 200 poundI and expected enterprise to keep 100 pound of the 200 pound to pay the excess which would leave me with 100 pound to be returned to my credit card account. Alas, this has not happened, enterprise have seen fit to stall for a period of two months so far and hav not returned my deposit.
I have had emails from their most senior employees (five in total) but still no satisfaction. They really don't seem to want to return my 100 pound nd that is all I want.
I will keep you all informed with the the result from the government authorities wher I am heading next.
They have had long enough.