This issue has been mentioned quite a few times before on here (no filtering for withheld numbers on BT phones with trueCall features post-switchover)
You are unlikely to get any help from either VM or BT since neither has any vested interest in investigating or fixing the problem.
The trueCall technology in the BT phones is licensed by trueCall but it is hard-coded into the phone with no means to update it and make changes AFAIK.
The separate trueCall device
https://www.truecall.co.uk/category-s/116.htm
does have the means to be updated where trueCall support have been able to 'dial in' remotely (via the phone line) to the trueCall unit and tweak its settings to match the VM line conditions and caller ID type. There have been several past topics about this on here.
The trueCall unit itself is fairly expensive at £109.99 but second hand units crop up on eBay at much cheaper prices. There is an optional £20 subscription (free for the first year with a new unit if I recall correctly) which allows you access to a web portal to configure and monitor the unit. You may possibly need to use the subscription to get support on a second-hand unit so check all the details above with trueCall before purchasing anything.
One past suggestion for the BT phones is mentioned here
https://community.virginmedia.com/t5/Home-Phone/TrueCall-phones-announce-feature-after-switchover-to-21CV/m-p/5325321
I believe others have tried the above but without success.
Someone has also claimed success with a complete reset of the cordless phones and base station, inc batteries out etc. (with the obvious likelihood of losing all your phone contacts if you can't back them up)
https://community.virginmedia.com/t5/Home-Phone/bt-premium-phone-call-blocking/m-p/5244630#M186037
Use any of the latter suggestions at your own risk, and with caution, to avoid losing any contact data and personalised settings in the phones.