I would sign up for the TPS anyway, but I would also consider activating anonymous call blocking too.
We have received a lot of calls from third parties over the last few months despite being on the TPS. I usually do the following on phone calls:
1. ask if they're selling something
2. find out company name and some other info if possible
3. ask how they got our number (they usually say "a local database")
4. tell them "well, we are on a database that means we should not be receiving these types of calls. Companies that do not check this database before calling risk being fined upto 10 grand. I'll give you 2 options... 1, I report your company and you get fined as you could potentially lose your job... or 2, you hang up now and I wont say anything".
the last phone call I had ended quickly with the guy at the other end saying "OK, bye"
Before the last couple of months, we've had basically no calls at all from companies like this.