Easy to join contract,hard to get out!!

I have been trying to cancel my paid up contract for two months,at 1st I was told I was in arrears so they have to make one more deduction then I have to call in and cancel .I called in the 2nd time nd I was told it will get cancelled but I've already been billed for the next month so I have to pay again.After this deduction I thought my nightmare is over but now Im told I have to put in a 30 day notice and will still get billed for the coming month! I am so disappointed I haven't had the sim for over since I lost it and couldn't do a simswap coz I forgot details of my last call and stuff ,I also think they should've done more to assist,now they just milking me out of money I don't even have.