Do you have caller ID? What showed up when they called? I've had Charter call wanting to do surveys and the number that shows up on my caller ID IS NOT anything remotely resembling a Charter number. Usually says some junk like Toll Free or something and the only reason I've ever answered it is jump down their throat and tell them I'm on the Do Not call list and to remove from their list.
Haven't had a call from them in quite some time now.