I guess it's a he said / she said.
The quoted fare is the final fare and has nothing to do with the traffic or anything other than a change in the destination or stops which you add to the route.
This comes down to a factual dispute between what you say the quoted fare was at the time you selected the ride and what Uber says it was.
You could respond again saying that and see where it gets you or you could dispute $4 of the charge, but some people find that their Uber accounts are locked out when that happens.