Double charged and due date changed unilaterally

Wow, where to start. My cell phone contract was migrated from Nashua to Autopage. I was double billed for the first month (Once by Nashua, once by Altech), when I queried, Autopage gives me a number for Nashua and tells me to contact them to sort it out. The number rings incessantly. Surely the new holder of the account should deal with problems with the switch over? POOR FORM! To try get a handle on the increased cost I request itemised billing, which was never done, but I have paid for. Now suddenly - after three months - the due date for payments is moved from the last day of the month to the 15'th. So on 26 March I am cut off because I'm late paying for March - which had not been billed yet and, well, hasn't ended yet. I have already started the process to cancel the contract. To add insult to injury, I now have to pay for the itemised billing, that I've never received, for the remaining 5 months outstanding on the contract as part of the settlement amount. You will never see/hear from me again. I'm done.