Hacked ?, spammed on voicemail | Technical service details | Consumer forum

Okay, I'm new to cell phones. I got the phone for emergencies about 4 months ago and a 7/11 speakout sim card and both work great.
I was stranded on the highway last week and used the phone. I noticed there was a voicemail notification for 1-647-530-1107. It appears to be some sort of spam about using wireless or having a home phone.
The problem is, now everytime I turn the phone on, I get a new voicemail message from the same number listed as being at the same time I turn the phone on.
So far, I've wasted $20 airtime listening to the unending voicemail and deleting it. It's almost as if my phone is sending the message to my voicemail.
I checked the number online, and it appears it's happening to a number of 7/11 speakout users.
Any suggestions about what I can do?
Thank-you