First, look at your modem. You should be using one you bought yourself. Their modems are older and may not be delivering the service newer models can provide. Here's a reference:
The Best Cable Modem for 2020 | Reviews by Wirecutter
The box will tell you if it's compatible with your ISP. Pretty much all are, the current standard is DOCSIS 3.0.
Second, look at your router. Newer routers now feature tri-band technology (one 2.4GHz and two 5.0GHz channels). Theoretical speeds for different generations of wi-fi are explained here:
802.11: Wi-Fi standards and speeds explained | Network World
I have a TP-Link TC-7620 modem (Up to 680 MBps down, 143 MBps up) and a Netgear Nighthawk R7900P tri-band gigabit router, compliant with 802.11ac. No problems.