Carpet Cleaning Questions And Stagnat Water Smell?

ok to make a long story short i recently moved out of my apartment into my new home. when leaving the apartment we had to have the carpets professionally cleaned which we did by a local mom and pop operation that the apartment management had recommended. we lived in a pet friendly community and had 2 dogs and i also owned my own carpet cleaner which we used on the apartment once every 2 months. i also carpet cleaned the whole apartment before i left. now after the mom and pop operation did their carpet cleaning as was required by the lease i signed the apartment smells like stagnant water really bad. the landlord is trying to blame us for the smell but i did the whole apartment before i left and there was no smell and now its rancid as for when we did the walkthough. does anyone know if its possible to have that stagnant water smell from in carpet from anything other than stagnant water? the landlord wants to blame it on the pets but its not possible as did the cleaning 1 week prior.