Hi. I have a fiber connection from excitel(100mbps)

I am getting very unstable connection especially with the 2.4ghz network on mostly all my devices... 5ghz seems to be working just fine i believe.... I have another hathway connection with technicolor modem router combo and tv is just working fine with that but as soon as i switch to tp link router, i m facing no internet or unstable internet.... I have narrowed it down that its something with the router.. Tried reseting the router, changed the channels and mode and ssid and password, tried making it open network... Enable TxBF, MU-MIMO... STILL NO GOOD.... please help....