Missed calls no caller id on Orange personal PAYG phone

usignuolo

I have an Orange PAYG phone that I use only for family and close friends.

However just lately I have been getting missed call alerts with no caller id, usually early morning or early evening. There are no messages left and when I dial Orange answerphone it says there are no outstanding calls and so I cannot delete it. Yet the missed call message continues to display for the next 7 days. The call history merely reports call time and no caller id.

Orange always sends me texts about its special offers.

Recently it rang when I had it open to make another call but I did not answer as it displayed the no caller id message and no one else should know this number. As it is usually early morning or early evening am I right in thinking it might be spam?