I lost my mobile phone

I have lost my mobile phone for three weeks now. When I find it lost, I stop my mobile phone temporarily.
Now I gave up finding it.
It is extraordinary pain. If I gave up my phone number, it is easy however if I try to keep my numbers, I have to pay £100 to sort out many issues.
Fortunately, my friend gave me a phone and if I make that phone activate on my contract, what I need to pay is just around £10. Since I have a bit hectic life now, I still leave it as it is.