I was going to suggest the same as Ocean Princess....are you usually good with paying your rent? If you are then I'm sure the estate agents won't be too fussed with you giving them whatever you can for the month then paying the rest in a few weeks.

I think it's probably best to pay off the debt asap without going on another payment plan as it seems your income can be unsteady at times. As others have said rentsmart are well within their rights, but that lady had no reason to be rude to you.