Change account back to 6 months

My account was a 6 months plan account from the day I opened it n when they amalgamated my account is now a 24 months account plan . I'm buying clothes on 6 months accounts not 24 months . Can I have it changed to six months as it was on six months before amalgamation. My account is also on credit but they keep charging me interest of which I'm not sure for what. Can I have this fix because it's just nonsense.refund all mu money taken as interest.