We have had four scam attempts on different Broadband lines to access our BT accounts. The calls are consistent and shows it's from 01455 335496 although this number is out of service, each time the lady who speaks with an Indian accent says that BT has detected multiple IP addresses accessing the Broadband service and we will have experienced slow speeds because of this and they will ask you to start a computer. This is an old scam but witth a new front end and much more credible than many. Sadly they cut me off when I asked for the offending IP addresses.
Have you tried to find out who calls? Well, at least you can identify the location of coming calls. By area codes. Check it out here https://areacodes.net/617. Maybe something will be more clear in this situation.