The best solution that I came up with was to contact the tenant to see if we can resolve it simply first.
If that does not work you should contact a real estate attorney that is familiar with local laws to determine what the next action should be.
It is likely an oversight by them. In your conversation with them it is important to be polite and professional.
Every state in jurisdiction has different landlord tenant laws. it is important as a landlord to be educated in these laws.
It is important that your lease is clear on who is paying for what utilities. If your lease is not clear and there’s a dispute, most jurisdictions will likely side with the tenant.