You don't have a good option if you won't believe him and he won't provide back-up: all you could do is refuse to pay, wait for the landlord to sue or try to evict you as applicable, and then in court, the landlord would have to back up the claim--and if he could, you'd have to pay anyway, or pay whatever portion he can support. And in the meantime, you'd have the stress, lost time, and possibly cost (if you get an attorney) of defending a legal action.For whatever it's worth in your case, I practice landlord-tenant law in northern and central New Jersey, and typical landlord legal costs are in the area of $150 - $750. While that's a wide range, you can see that, at least in my region, $275 falls within the norm, and possibly a bit on the lower side.