Sunnova Energy Corporation – Sunnova refuses to transfer the account to the new Owner of a property with the current HUD and proof of change of ownership with the County

Hello,
I am filing a complaint against the Sunnova Solar company that refuses to transfer an account that was sold, with at that time only a final bill balance due, and will not transfer from the previous Owner to the new documented Owner of the property. We have sent emails requesting over months and months, and spoke to the customer service over months which informed our office that unless the balance was paid the transfer would not be processed. We informed Sunnova the balance due is for the new Owner, but the account is still showing in the previous Owners name, and they informed our office they would transfer so the new Owner could pay the balance promptly. The transfer has not occurred and Sunnova is threatening collections which is illegal. Please advise.