We will not accept non confirmed cost in future.
***Not a teacher***
From a purely grammatical standpoint, I would sayWe will not accept non confirmed cost in future
We will not accept (any) unconfirmed costs in future
but to be honest, I don't really know what 'unconfirmed costs' are and I wonder if there is a more appropriate phrase for this. If you could give me the context, it would help.