Can my mobile phone provider hand out or sell my contact details to other companys?

Yep, they have every right to that info if you are in debt. And FYI, they will probably be calling you multiple times a day until you pick up and speak to them. I'm guessing you're in debt with them? You better take care of it now before they start reporting to the credit bureau or even worse, you default on this. Don't try to fight the collections agencies, they are more powerful than you.