Ghosts in my mobile

I have had a pre paid mobile for over a year now, as an extra phone. I brought it while doing some business last year to keep those calls separate, but I have been receiving the most bizarre calls and text messages on it over the past few months..none to me - just people looking for other people and calling that number!
Firstly, it was a series of calls being made to a member of some motor cycle gang notifying him of some 'gigs' that were happening. Asking for permission to 'come and watch the action go down'. These went on for a while - then a woman trying to find a friend to tell her that she had just spilt from her husband permanently and she needed some help and now a young girl texting to say that she knows that her best friend is under age and should not been drinking and has not heard from her for days and wants to know whether she is ok...I really need to cancel that number!!!