Such action would seem to violate contract law. In many jurisdictions telephone companies are specially regulated, and there are procedures which must be followed before service can be terminated for nonpayment. These procedures, and the remedies which are available under them vary considerably from one jurisdiction to another. In the US these are maters of state law, not federal. In Canada, I believe these are matters of provincial law.
A customer who has been disconnected without just cause could sue for contract violation, probably in a court of limited jurisdiction, such as a small claims court. But following the specific procedures for utility violations.
In some US states there is a "Board of Public Utilities" or some agency with a similar name that will accept such complaints. Some are more responsive to consumers than others. In some cases involving the officed of a member of a state legislator can be helpful, as such boards typically require regular legislative budget approvals. In other cases, media attention may be of value. The exact procedures available in the jurisdiction will matter a good deal. The current political situation may also matter.
