Hi @Najum, sorry you have not been able to get this resolved when you called. I've checked and we have your details on our queue and one of the team will be in touch once you reach the top of the queue.
I've used your suggestion and find that the number I want to keep is a BT number. I had a BT account with that number when I moved to my current address in 2007, but changed to another ISP in 2016 (couldn't get fibre at the time so a point-to-point system was established at the residential park where I live). The number was ported to an internet phone and the account is still open, so it shouldn't be a problem to change the new number BT have provided. Thanks for the tip.