CONTRACT EXPIRY!

I have had a contract with virgin mobile for about 6 years now and things have just gone from bad to worse! I cancelled my contract with virgin today so they tell me they bill clients a month in arrears, which i understand but now they want to bill me up until May 2015! Wow that's 3 months from now. I want to make use of a new network as virgin has nothing to offer anymore. So i ask them to make my number prepaid so i can have it ported to the new network as to not have to change my number. So they say i have to wait a month before the number can be prepaid which is not possible for me as i need my number active asap! I have no problem in paying what needs to be paid but they wont drop my number to prepaid until the 6 of March which is no use to me so i guess I'm now forced to change my number which is a huge inconvenience for me. Why don't they warn customers at least 2 months in advance so that should you want to cancel your contract in due time as to not sit with all this hassle! Virgin is just making my life difficult. Service and willingness to help customers is non existent!