You can buy a call blocking device or phone. Amazon has a nice selection..The T-lock Incoming PRO Call Blocker sells for under 60 bucks on Amazon and can block up to 1500 numbers.

its hard to say if its a telemarketer or not, many of those illegal ones use dialers and those can end up like this if there is not enough people to deal with the amount of the calls actually going out. Most of the numbers the illegal telemarketers are using are spoofed as a rule.  You can try filing reports on it though.

https://www.ftccomplaintassistant.gov/
https://esupport.fcc.gov/ccmsforms/form1088.action
https://complaints.donotcall.gov/complaint/complaintcheck.aspx?panel=2

Being totally harassed....calling many times during the week, all times of night & day, no one on the other end. Help!