New iPhone 6 won't call or text

Hello.

I just got an iPhone 6, upgraded from the 4s. I have set it up and used my iTunes to transfer data onto my new phone. I can use the internet.

However, I can't call or text. I thought everything from my old phone would be transferred including my old number, but I have a new number now for some reason. When I text it says "not delivered" and when I call I get a voice message saying that my account balance is too low. This doesn't make sense as I purchased an upgrade and got an updated contract.

What is going on. This is very frustrating.