It should most definitely react, maybe its just not a very obvious reaction visibly? Or maybe there wasnt enough water involved?
fumaric acid with ammonia should form ammonium fumarate... and if there`s dmt, that should become freebase.
I bet if you dissolve your dmt fumarates in water first, then add the ammonia to the solution, it should work, you should see some cloudiness forming. Then leave the solution for 3-5 days in the fridge and you should have your precipitated dmt freebase.
I suggest you take a look at the BLAB tek in the wiki for the fumarate to freebase slow water conversion, you can use sodium carbonate, and since the dmt will precipitate from the water which you will filter away, you wont have any significant sodium carbonate leftover in your dmt