Accounts are closed after a certain amount of inactivity. A time period after that, the number is released back into the pool of available numbers to be given out.
The SIM you have has also been deactivated after inactivity, so if you create a new account, you'll need a new SIM.
You could try and get the same number. There is always that slim chance that it was never reactivated for someone else but the odds are low due to T-mobiles large growth in new customers over the years.