Waterproof overshoes: am I using them right?
I've got a couple of pairs, and have had similar experiences.
The best I can do is with my better pair (with a reasonably tight but comfortable ankle strap) underneath my splash - resistant leg warmers. That keeps out a short heavy shower, or light drizzle for a few hours, but persistent rain always gets in (and anyway feet get sweaty in overshoes). Short socks (well below the ankle band) help as they don't provide a part for water to wick.
They'll never seal well enough if your feet dip in a puddle, even if, like me in winter, you tape up any vents in your soles. Even splashing from underneath can get in eventually.
The overshoes are still very beneficial in cold wet weather, as the water in there is much warmer than the rain, and wind chill is reduced. In warm weather I often don't use them (e.g. Saturday I was riding all day, mostly in rain, but would have been too hot with overshoes).
I only cycle in waterproof trousers well below freezing, as a third windproof layer over bike tights and running leggings. Even breathable ones are too hot and get very sweaty.   In fact, in summer rain I'm reluctant to wear any form of jacket.  Breathable ones are too warm and  aren't breathable enough, so I carry something thin and light, but end up just as wet from sweat.