Just tell them 'Please don't call.'
I did, and they don't.
I still get a nice followup email.
I have made it clear several times I prefer email communication, my "sales engineer" still calls. I work very long shifts that start in evening, calling me at 10:00 in the morning ends with me not answering because I'm still at work or because I'm asleep. He's only wasting his own time, so he can knock himself out. The call is always followed up by an email response from me. My family also doesn't understand that calling during daylight hours is useless so why would a company. I still appreciate the service they provide, as I can get things shipped to me on the same day of order even putting an order in @ 15:00 (or 3:00 pm for normal people). This means I have it next day usually by noon. Have to take the good with the bad.