For the cheque that you do have, don't just cash it, go to the bank it's written from and try to get it certified. That will tell you if there's $$ in there to cover it or not. I think there's a fee to get it certified, but if you can't do it there's no fee.
And if it can be certified, then it is and you are guaranteed to get the money.
In the future, security deposit cheques have to be cashed because you have to hold the security deposit in a specific way, check the landlord tenant act on how you're supposed to keep that money.
Yeah, people complain about crap landlords, but I can understand how some become so terrible.
I just had a tenant abandon a property.. unpaid rent, left the door open and left the place, bunch of their stuff left behind for me to deal with. Great eh?
Oh and the best part? They stole my fridge.