I had the same problem with my internet provider. After I told them I would cancel my account the next time they called me with another “exciting offer” they stopped calling. I’ve used this method successfully with several other companies I do business with. They don’t want to lose your business.
Note regarding ISP or Telephone Co calls:
If they continually call, don’t complain to the caller. That person is usually just a hired dialer who has a list of number to call. If you complain to them, they will just note it and continue on.
Instead, call the Customer Service number and complain directly to them. Insist that you be removed from THEIR sales calls lists.