Blocking Spam Area Code

I am receiving Spam calls from area code 806 and 737 (Texas) Multiple times in a day.  They call, goes to my voicemail, and record nothing (leave no message ) but stay silent for 10-15 minutes at a time.  This is to my Toll-Free number which then of course is eating up my minutes needlessly since they are just calling to perhaps meet a quota or pretend they are “busy” for their work purposes.  I want to block the area codes 737 and 806 as these are not areas that I service anyhow.  I do not want to be charged for “exceeding” my minutes when there isn’t even a real conversation or message that is being left.  If I cannot block an entire area code (blocking one specific number will not work as they randomly call from another random number just a couple minutes later, but seemingly area codes 806 and 7373 seem compromised), then can I make my voicemail drop a call or stop recording after a minute or two of silence (no message being left) so that my toll free minutes are not being wasted unnecessarily?