You need to give more info then that. You posted under the mobile section so is it safe to assume you're talking about a mobile phone service?
Did you port your number over or sign up a new one? What was on the bill you received?
The agent of my new provider who did all the porting and chatting with Optus Agent and said that I only need to pay $ 90 plus.But Optus sent me a bill of $250 plus due on the 21st June.