I had a phone on contract and I said I was 18 and I'm only 17 I've got it in a different name will I go to prison

Your parent(s) or guardian is/are liable for your financial doings as a minor.
What happened - did you sign a 1 or 2 year contract and stop paying?

2 years year contract and I am still paying for it I turned 18 2 weeks ago

Yesterday, you wrote:
... I'm only 17 ...

Now you write:
... I turned 18 2 weeks ago

One of those statements was incorrect. Which?

As long as you continue to pay it till the contract is over, nothing happens.