Mweb Fibre really sucks 20mbps on 50mbps line

Can someone please advise how I'm never getting 50mbps speed on my Fibre line it's always 12mbps or less I have a mesh as we have a duplex but we always get buffering or YouTube playing like 8bit games graphics can we please get a proper explanation cause paying almost R1000 for a 50mbps line and not getting 20mbps is very bad with 3 people in the house that's very bad and changed router also still the same problem is there any other solution than getting a different provider for cheaper but still the same line speed