What the "other guy" had is irrelevant.
He didn't sign your contract. You did.
Whether it's a "jet" type rating is irrelevant.
You signed a contract. Whether 18 months or 2.5 years, did the contract not spell it out? Were you not aware of what you were signing?
I have walked away from jobs with zero in the bank. You could, too. You chose to sign the contract, you agreed to the commitment.
Your assertion now is that you were type rated in the airplane, but are not flying the airplane. Your contract was for the type rating, and did not specify that you were guaranteed to fly the airplane, correct?
Do what you agreed. If you agreed to work for a period of time, do that. If you can't do that, pay it out, and move on. Done.