>>/957844/
> i disabled the modem's DHCP server function and nothing broke.
You have established a connection, nothing will break unless you restart either device. Without a DHCP server the network will break, the network may also break with two DHCP servers.  

> DUno what the VLAN thing is
Depends on your ISP and the connection type. A VLAN allows different ISPs to use the same network. The network is segmented by VLANs. 

> I am running a digital voice protocol that other peoples devices need to have that port open to call me and vise versa.
You should create a specific Firewall rule that only allows this traffic. Even then this is probably not going to end well unless you have a specific allow list of hosts. 

If it is a common port for a common service, chances are people are scanning for it. How are these people authenticating? Otherwise, I congratulate you on your new C2 network.