I have some sympathy for you having been a Vodafone customer before.

Did you eventually get a new phone or are you using the nearly new phone still?

Have you spoken to the complaints department. 03333040441

If you want to escalate to to Ofcom you will need a letter of final response. You will need to out your complaint in writing to Relations Manager, Vodafone Limited, The Connection, Newbury, Berkshire, RG14 2FN

Your formal comment needs to be a lot more succinct than here.

"I ordered a phone. When it arrived it wasn't what I was expecting and I feel the description was misleading. You offered to modify the contract by allowing me to return the original phone and replace with a different phone under the same contract terms. You did not collect the original phone or replace it. You are now billing me for it. As you did not keep to the terms of our new contract, please collect the phone and cancel the outstanding bill within 14 days".