I had a summer job in a telemarketing sweatshop and I learned that you should be polite to telemarketers.
At the time, at least, the company I worked for had two "call back later" lists. If the telemarketer didn't reach a human (because the phone was unanswered or went to voicemail), the phone number would go on a "call back next week" list. If the telemarketer reached a human who said "no thanks", the phone number went on a "call back in six months" list. However, if the telemarketer reached a rude human, their phone number would go on the "call back next week" list, just to spite the person. :\
Also, you should ask to be added to their "do not call" list. If you ask to be removed from their list, they may oblige, but they are likely to remove you from "that" list and conveniently not bother removing you from the master list.
At the time, at least, the company I worked for had two "call back later" lists. If the telemarketer didn't reach a human (because the phone was unanswered or went to voicemail), the phone number would go on a "call back next week" list. If the telemarketer reached a human who said "no thanks", the phone number went on a "call back in six months" list. However, if the telemarketer reached a rude human, their phone number would go on the "call back next week" list, just to spite the person. :\
Also, you should ask to be added to their "do not call" list. If you ask to be removed from their list, they may oblige, but they are likely to remove you from "that" list and conveniently not bother removing you from the master list.