I had one like this a couple of years ago. Happy with clean but not the smell. I went back, hands and knees job - defo sweaty feet smell, and I told him. Also checked the stair carpet, same type etc. that I cleaned - no smell. He walks around in his socks. I sprayed and brushed in some deodoriser, after telling him it was nothing to do with the cleaning or the stairs would also smell. Obviously spends more time downstairs. I advised him to wear slippers and left him some over-shoes until at least, completely dry. Nothing else heard.
By the way, if nothing else works out for you, they are only entitled to the value of the carpet, as it was, immediately prior to you cleaning it, not a new one.
Dave.