It's just the PikePass customer service line. They will call you if your account has been in the negative for a while, or goes into the negative exceeding a certain amount. Nothing to really worry about though. The customer service is friendly, and they're willing to work with you because they want to keep your business.
This is the Oklahoma Turnpike Authority calling about your Oklahoma PikePass account. They'll call you if you let your account run into the negative. No big deal. Just make sure you either talk to them and bring your account into the positive, or go into your online account and bring it into the positive. Otherwise, they'll shut your PikePass off and every toll booth you go through will result in a $90 ticket.