I signed a 2 yr contract & it must end after 2 yrs

My contract with Mtn expires in September. I want to let them know NOW that they must not role it onto a month to month contract. I signed a two year contract and I want it to end after the two year period. I have spoken to 4 agents at the call centre and to an agent over email, all of whom tell me different things. The first agent told me it was sorted. I phoned again to double check and the new agent told me that the note just reflected that I asked for my cancellation date but that now it was sorted. I then received an email that said that I could only inform them that I wanted my contract to end (at the end of the contractual period) one month in advance. I then phoned again and was told by a new agent that although there is a note on the system of my request that I must still call again at the end of August because \to be honest