These faxes are the result of an honest mistake, not some nefarious plot to annoy you. The faxes are coming from a large legit healthcare company called Athena Health which provides "EHR" Electronic Health Records services to medical providers.
Somebody must have mistakenly entered your phone number, intending to enter the fax number of a medical facility such as a doctor's office. Athena's fax server is trying to send health information such as medical orders, prescriptions etc. You won't be able to find out who accidently entered the wrong phone number by hooking up a fax machine and reading the "from" section of the fax, because the first fax Athena sends is a one page fax from Athena asking you to verify that you are a legitimate healthcare provider, to avoid inadvertently sending sensitive medical records to the wrong fax machine.
Whoever screwed by entering the wrong number up is probably sorry, especially since they risked violating HIPAA laws regarding patient information. After a few attempted fax calls, Athena will give up and tell the sender that it didn't work. The problem is that the same mistaken sender, after getting the error report, may try to send it to the wrong number a few more times until they figure out that the number is no good.
You may be cursed with a phone number that used to be a medical facilities fax number, or is the same as a medical business' fax number except for one number. So, until medical facilities update their numbers, you will be plagued by fax calls.
You can call Athena Health at their main number shown on their website to tell them the problem. They are a good company; I deal with them all the time. They will do their best. Maybe Athena can block your number. If they haven't set up the ability to do that yet, they should. The problem is that after Athena blocks the number, some other healthcare EHR company with the same incorrect information will start the same problem all over again.