Hi Dotnet,
Here are a few possibilities.
You could put all calls through to another number till they stop.
You could get another sim card.
If you can get hold of the other phone, you could remove your number
then return it, but theres no telling if its been written down.
I would think that getting another card would be your best bet.
It would mean calling all your contacts and leaving a new number.
After a while you could try the original card again, to see if the
problem has gone, if not just try again after a month or so.
Don't forget, if you dont use the card for about three months
(i think) then you may lose that number, but that has been changed
recently, it may be six months now.
Maybe you could visit again, and adjust the phone memory covertly.
Best of luck, John