Jonny
Of course you have rights. Dealing with these large companies can be painful once things have gone wrong.
Vodafone have not contacted you for months, as they are probably negotiating selling the debt on. The debt companies either chase money on behalf of creditors or they buy the debts. The debt companies that have contacted you so far, probably just had a list of outstanding accounts from Vodafone to chase.
What you need to do is make an official complaint to Vodafone head office Vodafone House, The Connection, Newbury, Berkshire RG14 2FN. Send a letter to their Chief Executive by recorded delivery setting out why you believe the contract was miss-sold and what problems you have experienced since. Ask them for full details of the account including a copy of your contract, advising that you will contact OTELO to look for their help, if you are still unhappy.
Huckster