This is mainly a peer to peer support forum.
Have you contacted support to see what they are billing you for?
Did they dispatch a technician to your house for repairs?
If so, what did he find/repair?
Not saying it is your fault or charge is valid?
That info will help determine if charge was proper.
For example (not saying this is true in your case):
If you had damaged ONT, they could charge a repair fee.