The TPS is just about useless. They have very little power and are nothing more than a paper tiger. Foreign companies don't have to abide by the TPS rules, and lots of British ones ignore the rules as well.
That is why my phone is permanently "off the hook", from about 09.00 to late in the evening. That way if there is a family emergency in the middle of the night, they can still get through, as happened in February 2013, when my brother had a serious accident and head injury. Its a pain in the ar*e but I can't think of another way to stop these nuisance calls. If I forget to take the phone off the hook in the morning, within 10-15 mins the calls start again ! Its a modern plague.