Changed to pre-paid without my authorastion

I had a data contract with Vodacom which was expiring at end Feb 2016. I asked Vodacom to please cancel that contract and despite the fact that the contract had a separate sim card and separate number, my regular cell phone number was changed from contract, to pre-paid without my authorisation. As a result, I have not been able to use my phone (which I use for work purposes) for the last week. I have been calling in since 29 Feb to try and make head or tail of what is going on and the only thing I have been hearing is that the problem has been 'escalated'. Yesterday (Sunday 6 March) I chatted to a lady who gave me the email address for Daylan Govender in the retentions department at Midrand. I had to send him a mail explaining the situation but even though I confirmed his email address twice, the mail came back as undeliverable. I have spent hours on the phone trying to sort this mess out and I am getting nowhere. I have had the same cell number with Vodacom for 20 years and I have NEVER owed them any money. I am so ****ed off and think the only way forward is to migrate my cell number to another service provider who will be happy to have my business.