They keep calling and then hanging up.

Caller told my husband that I had "assisted" them in a market research call & then asked to bring out an air filter system.  1. An unidentified so-called market researcher called a couple days previously & asked me about allergies, asthma, etc. in the family.  Told him we had none.  (Tho we do)  2.  Believe that call was a "set up" to approach us with a sales call.  We are on the do-not-call list & these people are obviously cooking up schemes to get around that.