Blocked numbers' calls still come through

I am currently under assailance of incredibly pestidious telemarketers that call me at the top of every hour, to the point of having literally ripped out a tuft of hair from my head. --- I block all the numbers, but they keep changing the numbers they come from. However sometimes I still get calls from those blocked numbers, they ring the phone, and when I go to block them, I see it's already blocked, and that indeed that number had called me before! There are so many numbers I have lost track and count, so I'm not sure if it's just 1 bugged number or a variety of them. I have tried unblocking and blocking again, to no avail.