Having done some digging, I found this - https://community.bt.com/t5/Archive-Staging/record-of-incoming-landline-calls/m-p/2244279#M1101985 - which suggests the expectations you have, were part of an additional BT Retail phone service option, which was withdrawn in 2020. BT Call protect has always been more sophisticated than the handset only option from Plusnet.
You might be able to request such information (if it exists) under a FOI request to Plusnet on what information it holds (if any) on inbound calls. I would suspect that Plusnet (who do not run the telephone systems) only have details of outbound calls for the sole purpose of billing. They have no business reason for holding data on inbound calls and therefore under good GDPR practices, it can be argued that they should not have that information.
BT Openreach however might have such information, which the constabulary ought to be able to acquire, far more easily than might you / Plusnet.
In the short term a handset capable of storing the last 30-50 caller's numbers (if not withheld) might be the most pragmatic way forward. Even if Plusnet could give you the information you want, the details of call where the number was withheld are only likely to be obtained by a court order or police warrant. Such information should be in BTOR's call routing records but would be considered sensitive information, not to be disclosed unless legally forced to do so. Even where the display CLI is spoofed, the originating CLI should be known.
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
