I just tried deleting my account and it said I owned them money I don't have
Agree on this. In general everything is very shady on this. Doing like something is free while it is not (At least I could not see anything "free" on Deepinfra). Than Deepinfra itself not really telling you you have to directly pay without even given them any billing information or extra confirmation on prices (is this even legal I dont know?).
Luckly I was fast enough to realize it so not really lost something but if you dont want to come out as a shady developer you probably should not give out deepinfra as free or deepinfra at all in my opinion.