Typically it is not possible to disable TR-069 so long as a router is running the ISP branded firmware. You may be able to firewall off Port 4567 by creating a custom firewall rule, while the router is disconnected from the Internet, which disables the ability for the router to be managed in most cases. That won't prevent it from phoning home, which is typically handled via HTTPS.
The sure free way to remove TR-069 from your network is to use a third party router, which works if you only pay for Internet access.
G1100 should support SSH. I believe it can be enabled from the Advanced > Remote Administration section still. SSH may have the same command available.