Welcome to BBR.
Bonding requires support at both ends of the connection so your ISP needs to support it. Need to talk to them.
If they do not support bonding/multilink get a load balancing router that supports as many connections as you have. The load balancer alternates sessions between each connection. Each session is limited to the connection it is using but total throughput will be the combination of all the connections.
Load balancing only works for connections initiated by devices on your network, ie browsing, streaming, etc. If you are running a web server is has no effect since that connection requires folks on the Internet know the server IP. If you need more bandwidth to run server consider using a hosting service.
Los Angeles, CA
Support from an ISP isn't really needed anymore, but you're correct, there's a need for a point to point connection.
We can overcome this limitation using GRE tunnels, similar to VPN tunnels and works by establishing virtual tunnels over multiple internet connections and then bonding the tunnels together logically (at layer3)
This provides true bonding and the ability to use the total aggregated speed on any single file transfer. Since it's VPN/GRE style, there's just one IP address and server hosting from bonded connections is very possible. It's made simple using a public IP address although NAT options are available.
We call it vUnity, google it.
Let me know if I can answer any other questions,