Weak WiFi speed and signal

Am having hard time with openserve each time their offices take hours to answer their phones am frustrated because of weak fibre wifi signal and speed I can't even connect in the other room after they told me I can get speed up to 20Mbps but I always manage to get 0.9 Mbps if lucky 1 Mbps am so unlucky I don't know what to do anymore even speed test failed to help