SMS sending but marked as "not delivered"

[Codenutz]

Wondered if anyone can help me 

I just switched to vodafone from o2 but since doing so my SMS sending isn't working properly.

When I send a message or always come back saying "Not Delivered". Weirdly the message always get delivered.

I've had this happen work several different numbers / people. All regular mobile numbers. Tried turning off and on, removing the sim etc, but still the same deal every time.

Any clues?

[Codenutz]

Seems like I may have resolved this myself! It looks like my iPhone wasn't recognizing my number after it was transferred from o2. Had to reset the network settings and now all seems to be working.