My 2 cents
I believe integrity and reputation is something that one should always protect and it irked me to have someone accused you of stealing when you didn't (I'm assuming you're innocent), especially if they claim proof but don't show it
I would be very upset if I was in your position, mainly since I have undergone a security clearance and the RCMP looks pretty far back into my past. If they would have uncovered I was let go for stealing (and I was innocent), it may reflect badly on my character reference
Anyways, I'm just argumentative and not good at taking criticism, but maybe you want to go with that thought, and say you take the accusation very seriously as it may affect your career (say law, government...etc) and that if they don't show the proof, you'll be force to pursue other means.
Layoff because they want to reduce their payroll I can understand, but a false charge is something I wouldn't go down without a fight
but that's just me
If you want some answers and you are completely confident you didn't have any wrong doing, perhaps you can