This is the K12 automated phone line for equipment return. You might have received a computer, monitor, laptop, and/or accessories at the beginning of the school year.
This is an automated call you receive after your child disenrolls from a K12 program. It reminds you to return the equipment, and gives you the opportunity to receive additional free shipping labels should they be needed.
They do not call that frequently, once or twice a week perhaps, and they do not call at annoying times.
If you're receiving these calls and do not have a child enrolled with an online school, I would recommend going to the K12 home page and calling the main number for help getting your number removed.