Relentless spam calling from different sequential numbers

Cold calls me incessantly from 13+ different computer-generated phone numbers that resemble landline numbers. Using new numbers each time makes blocking them ineffective.

Given the timing of their harassment, I strongly suspect that they're guilty of some very sketchy practices concerning data privacy, e.g. buying personal information from mortgage lenders/credit bureaus and have reported them to the National Information Regulator for possible POPIA violations.