Thanks for using the forums to get this issue with your Mum's number change looked into, I am sorry she's been getting these nuisance calls. I would be more than happy to look into this for her.
We can help change her number over the forums, we'll need to go into a PM first in order to get it changed.
Before I send it over though, I am aware that change a landline number can be stressful with giving the new contact info to lots of different people/companies. So I just want to send you a really helpful and informative link about scammers and nuisance calls 👉 Block Nuisance Calls - Which may help before we go ahead with changing anything.
If you want to take a look at the information outlined in that link and get back to me if you & your Mum still want to go ahead with the number change, we can do!