Why do I get missed call notications even why my phone doesn't ring?

Hello,

I have a Nokia Lumia 625 and recently I've been getting notication that I've had missed calls even though the phone hasn't rung. this happen every 1 in 8 times or there abouts.

Has anybody else had this issue and if possible how you rectify this?

Regards,

That typically happens to me if I have poor/no service. It notifies me that I missed so many calls while I was out of service.