can get contract cancelled.

I got a contract from virgin mobile and have 2 phones on one contract, my contract expired in feb 2015 for the one phone and at the end of august for the other. I phoned to say they must cancel my contract, they wanted to give me some other phones witch i then declined. I send an email with the proof of my last payment end of August, and a letter saying i want to cancel. Now they blocked my phones because i didnt pay it this month. Im not going to pay anything, When i made the last payment in end august they also blocked my phones. i told the customer people then that i still have enough money on both my phones. they then reactivate after proof of payment was received. now they said i must pay again. help...help!!!!!!!!!!!!