Have you tried clicking on 'Send feedback', the very small link on the bottom right of the map?
I did when Maps was failing to route through a junction near where I lived in London, because it thought going straight through wasn't legal (it was). It was fixed a few weeks later.
(Disclaimer: I work for Google but nowhere near Maps, and my experience of correction predated my employment. And I don't speak for Google.)
Where Google Maps has a dedicated way of providing corrections, you can get things fixed quickly.
Where it doesn’t, and you have to use a more generic feedback form, my experience is that it never gets corrected. Zero times out of perhaps a dozen that I’ve tried, for several different types of errors (misplaced town markers, a missing consonant in the Bengali spelling of a road name, can’t remember what else off the top of my head). I just don’t bother now. Most seem to get fixed some years down the line, probably incidentally as part of some other more generic data or processing algorithm update. The only time I’ve had any sort of prompt success was when I reported something on a Google Maps-related HN thread: https://news.ycombinator.com/item?id=23367961. The fix in that instance was evidently done as a one-off exception, but looking at a few places in Google Maps now, I think the underlying systemic issue is finally fixed (for now).
As far as I can tell, that feedback goes into a black hole. I've sent many corrections there, not a single one has been adopted, including ones where entire streets didn't exist (i.e. they exist on Maps but have never existed IRL).
In the city I used to live, they had to put signs up at the entrance to a street, warning people to ignore Google Maps. It tried to route people the wrong way up a one-way street, and the government had failed to get Google to fix it.
I did when Maps was failing to route through a junction near where I lived in London, because it thought going straight through wasn't legal (it was). It was fixed a few weeks later.
(Disclaimer: I work for Google but nowhere near Maps, and my experience of correction predated my employment. And I don't speak for Google.)