God will most certainly repay you, but not necessarily materially. What merit is there to give a donation with the full expectation that God will pay you back? Sometimes He does. I've also had situations where I almost immediately received back the exact amount I had donated. But God gives that more as a sign (message) about how pleased He is with the almsgiving.
Last year a guy I know had a small crew of landscapers working in an area of his yard that the sun beats down on and never has a breeze, it was sunny and in the upper 90s that day - it was hot! Knowing it was going to be a hot day, he had put all the small bottles of water in the fridge that he had on hand ahead of time, to give to the workers in case they didn't bring any with them.
Well, while they were working and sweating away in the dust and the heat, he went out and gave them each a bottle of cold water, never really thinking much about it other than he figured that being so hot and dusty that it would be a nice thing to do and would give the crew a nice little break to quench their thirst with some nice cold water. After having given them the water as he was walking away, he apologized that the bottles were not the bigger ones, but we were both a bit dumbfounded when they thanked him as if he had just given them each a $100 bill or something. To say they were thankful would be putting it mildly.
The jist is, we never really know just how badly some people need, that which they do not have but we may freely give to them. So I wonder if our reward will not only be due to our true charity, but if it also includes or incorporates the necessity, or urgency, or the degree of appreciativeness or greatfulness on the part of the recipient, of which we often have little or no knowledge of.