Welcome to our forums and thank you for your post. I'm really sorry that you've been receiving unwanted calls, I can certainly appreciate the frustration!
As many of these calls will be automated, or will originate from a dialler which generates random numbers to call, we can't always guarantee that a number change would stop this type of contact. There are a couple of other things you can try, if you haven't already.
First of all, you can always register for the Telephone Preference Service (TPS) which is a free, independent service to restrict unsolicited calls. You can find plenty of information about the TPS on their site.
We also offer Anonymous Call Rejection as a landline feature with our packages, which would stop incoming calls from callers who have blocked, hidden or withheld their number.
If neither of these are suitable for you, please do let us know and we can take a look at your account with a view to assigning a new number.