I found out that the best way to force Google Maps to update is to make the correct edit in Open Street Maps. Google seems to source its local information from there.

Just an anecdotal example: I live at the end of a cul-de-sac, and I’ve seen loads of cars drive up to my house, and then gingerly do a 15-point turn (the road is very narrow), and drive back. I checked Google Maps and found that it lists my street as open. I’ve filled reports with Google several times, and nothing happened. Then, I updated OSM to indicate that at the end of my street there’s just a pedestrian footpath to the next street. Within two weeks, the number of cars turning around decreased drastically. I checked Google Maps, and found that they fixed their map. A few years later, there’s still the odd car making the mistake, but the only map service I could identify that still didn’t update was Apple Maps.

Since then, I’ve done several edits in OSM (I live in a young estate, with loads of construction still going on, so maps are not very reliable), and Google always picked up these edits.