Landlord keeping a deposit?

It sounds like they are taking definitely taking advantage of your situation. Unfortunately too many landlords dare depositors to take them to court and the law does not punish landlords severely enough for this to be a preventative measure. Most important is to look at the words on the contract.

If you really want to look at words, if you are guaranteeing that the landlord will receive cash on a certain day, then a breach by a third party that causes you to be late with providing them with cash may give you a remedy against the bank who may have caused a breach by you. I would think that it does not require cash. It may say that payment must be made by a certain day (offering a valid check would qualify as payment) and that the error that occurred at the bank did not affect the validity of your payment on that day. But this probably isn't about law unfortunately....

They should give you the 550. If they completely refuse and will give you 400 without signing anything, then you might want to take it and sue them in small claims and ask for punitive damages. Report them to your local governmental authority (you should find a dept. of housing online). Beware of any check that says "paid in full" or some other statement like that or else you might be precluded from suing for the rest. Small claims is a good remedy for something like this. It's cheap and you can inflict damage against unscrupulous people and you should catch a sympathetic ear.