Hi there Andy,
Ok the same thing happened to me.
I originally changed my number because my ex got hold of it and was phoning and harassing me, then passing my number on to all & sundry. So I told Virgin and they changed my number.
The very day they changed the number I started getting calls for an unknown person, from collection agencies. They wouldn't believe me when I told them I had just acquired the number and didn't know the person they were after. The cheeky sods started quizzing me and asking my name, my address etc. I gave them a phoney name and address because no way were they going to treat me like I was a criminal and a liar. They said the calls would stop.
The calls didn't stop and I had to keep my answer machine on all the time for over a week.
I made sure my number was still registered with the TPS and even reported the nuisance calls to them, but that didn't help. So I called Virgin again and told them the calls had been coming in for over a week, at all hours of the day and how the callers wouldn't say anything if I picked the phone up...just leave messages for the unknown person, and how my health is bad and I couldn't stand the stress any more.
Anyway, I got it sorted. Virgin were very understanding, especially as I have been with them for over 10 years. They gave me a brand new numberfor free...not a recylced one, a brand new one. One which I got to pick myself. They asked me to pick numbers between a certain range, for each digit, and then they activated my new number within 24 hours.
I've had no nuisance calls since.
I know it's rotten, but you're likely going to have to change your number again.
Hope this helps!
Suze