Cancellation of Nashua Mobile contract

I had a contract with Nashua mobile. Autopage took us over since last year November 2014. I use to pay my account on the 28th of each month. Suddenly my line was cut cause I did not pay by the 15th of each month. Last month when I did pay my account on the 13th of April 2015 and also send the proof of payment to accounts department, my line was cut AGAIN yesterday. When I called them they said they did not receive payment. I had to send proof of payment AGAIN before the activated my line. My contract with Nashua expires on the 30th of May 2015. I contact Autopage to give them calendar month notice and told them that I will not renew my contract with them. They told me that because their calendar month works from the 28th until the 28th of each month I will only be able to make the final cancel date on the 28th of June 2015, which is 2 months notice. I never signed a contract with Autopage and now I need to play by their rules which this is unacceptable. Then they ask me why I don't want to extend a contract with them.mmm. According to legal advice they can't change things as the pleased they have to stick to my Nashua contract.