still paying for an expired contract

so after 24months my contract is supposed to go on a month to month. i get my bill to say my contract is paid up and that going forward my subscription will decrease monthly. they have however decided to charge me the full subscription one pays to pay off the handset and claim that my contract ends april and not march as they so brightly in red stated on my statement.<br> so no that i'm querying this and refuse to pay the full subscription i'm getting conflicting information and it seems my query is being deliberately dragged out so that my debit order can go off. i've sent them proof and my contract was changed and yet no mention of pro rata payment and whatever services i am going to be charged for i have not been privileged to receive the entire month. <br> Clearly this is a method to get money out of me - someone who has been a loyal subscriber for 11 years never missing a payment.