Your current dish would not be suitable for 2-way internet, but might be used for a receive only using a phone line for the up channel (if that is even available anymore). One would need to identify a c-band internet provider willing to provide a package to a single user. To be a two-way satellite system (UP/DOWN link) the service would only be activated using a fixed dish with current 2-way compliance.
A C-band Internet service is typically installed and certified by an authorized technician. On a two way system, once the service is activated, the user might get away with adding sidecar feedhorns for receiving a few satellites on either side of the centered feed/BUC. On a one way system, the dish could be motorized for reception of other programming, but would need to be parked on the providing satellite to establish an internet link.
KU or KA delivered satellite Internet will be much less expensive to install, easier to subscribe and less problematic to maintain and less cost to service.