You asked...yes, she lied.

The obvious response from you is what can you do about it?

Answer, nothing. Once you signed the contract, no words from any sales person count. You company discount is likely 15% - as are most...and they only apply to a small portion of your bill.  You may save $5 on a $60 plan. 

You got what you got....and you have it for 2 years. It is in the contract.  Only T-Mobile will pay your 350.00 ETF to leave...

Good luck.