They are with Avalara, a web site that offers free sales tax rate information. If you are selling something and aren't sure what rate should be charged at the location, you can look it up by the address. They offer 50 free lookups. Someone with your phone number may have registered with them. The call is just a customer service follow up. I haven't bothered to answer because I have no need to speak with them and don't want to waste cell phone minutes, so I think I'll go to their site and opt out of these calls.