First of all you need to get rid of the 'extortionate interest rate' card. You will most probably need to break it down to two or three 0% cards (depending on your income). You can easily get hold of these via various credit card comparison sites. Once you get into a situation where ALL of your repayment is going to paying the loan off it shouldn't take that long to pay off this debt. You may need to switch your interest free cards over to other 0% cards when your interest free period runs out, but that is the name of the game. When you get your 0% cards and the new accounts have taken over your old, expensive debt, cut them up! In fact cut ALL of your cards up until you have paid off what you owe and can see the wood for the trees.
Good luck.