Charged double interest rate on one account

I've been with Edgars for more than three years now and I've never had any problems with it until now due to double interest billing on my account.<br> I've recently noticed that I've been charged double interest on my account since last year yet I made a request for my account to be on the 12 months plan.I wrote an email about my problems and asked if they would explain to me what is exactly is going with the monthly billing and I was simply told that all of my previous purchase has been ran on both 12 and 20 months plans and that it now be on 12 month plan .So I would like to know now is am I getting any compensation for this\mistake""