If you were lead to believe you had to have it it was mis sold. If you didn't really need it ( even if you asked for it) it was mis sold. If they didn't ask about your medical history, it was mis sold (many policies have extensive conditions when they wouldn't pay out anyway).
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
The fact that you thought you had to have it means it was probably missold. There are numerous reasons for misselling and now the banks just seem to pay out.
I think some solicitors argue that if the PPI payments had been used to reduce the balance then the client would not have had as much interest to pay on the outstanding credit card balance. They would then argue the interest repaid should be at the rate of the interest charged but that is for lawyers to fight!