I'm being charged for someone else's account!

I had a Neotel account very briefly almost 2 years ago. After being retrenched I had to give it up. However during the past 7 months I am receiving billing information on a daily basis. I have queries this with them and was told that my number was reallocated to someone else. They promised to change the details to the new subscriber but I am still getting daily billing reports, and the new client is really clocking up the billing amount.<br> This morning I received an sms from a collection agency/attorney threatening me for non payment of the account. Obviously nothing has been done about this new client. I simply cannot understand how they can reallocate an account to someone else without changing the relevant and very important details!! I NEED THIS HARASSMENT STOPPED IMMEDIATELY.