Some ISPs are known to cheat and give speed-test websites preferential treatment so that the speed looks fine when testing.
Also you are likely on a cable-modem, right? These are a shared medium, so those 1000/50 numbers need to be taken with a huge grain of salt as it highly depends on how much other people in nearby apartments/houses are using it.
Try if at all possible to switch to a home fiber connection, as those offer much more consistent connections and usually also higher upload speeds.