hi, i received my first t-mobile bill and its double the usual line rental for the first month, the second bill was taken as normal.

Is it usual for T-mobile to charge twice for the first bill and is there any reason for this?

Yes it is normal for the first bill to be double. You should have been told this by the person who sold you the contract.

You will get the money back, I can't quite remember the reasoning behind it now as it was over 3 years ago since I took out my T-Mobile contract (now on O2), but I was made aware that the first bill would be double.