Received as an answer to a for sale ad. No answer on other end.  Now constant texts and calls with no voice.

This sounds like the Craig's List/Kijji scam.  You will be sent more money than needed.  The buyer will want a "shipper" paid by Western Union.  The shipper is the scammer & the check will eventually bounce.  Did the buyer say he was at sea, in the military, or a similar excuse?