I don't know how many ways I can say that over a period of eight years we tried every technique possible to stop one particular brand of nuisance call (one where the caller repeatedly asked to speak to a Mrs Clements). We were polite. We were rude sometimes. We tried leaving them on hold. We asked to speak to supervisors. We spoke to supervisors. We got them to look up the physical snailmail address of the person they wanted, which didn't tally in any way with our address (including area code). We talked to BT. We were in any case ex directory and on the TPS list. (Which of course didn't help because they were asking for someone else in the first place). We tried being funny. The calls continued.
Please accept that this is my experience. Your experience might tell you that by being polite you have stopped the calls. Whoop-di-doo for you - we're still being harassed. Now, as I said above, we're at another number and now we're being asked for another name instead of Mrs Clements, but the same situation exists. My husband is currently also getting frequent calls from insurance companies in relation to an incident four years ago which didn't become the subject of an actual claim because it was easier and cheaper by far to fix the damage ourselves. The calls continue despite the number of times he has patiently and politely explained the situation. He's driving a different car now, with his insurance with another company. Makes no difference to the serried ranks of callers with his name on their duplicated lists.