Reliance Home Comfort review: Rental water heater

My rental on-demand water heater ruptured on Nov 30 on 2024. I called for service from a company listed on a tag on the water heating device. The firm responded, indicating the device was listed as under warranty and they would attend to it. They made an initial visit and assessed the issue, indicating a repair was needed that required ordering a part, which arrived and was installed in mid December.

March 11th, i was contacted by the service company asking for information on my device and after a brief discussion it was realized that my device had been owned by a company that had been bought by Reliance Home Comfort. the service company reached out to Reliance but were told that only the homeowner should do so. I contacted them and after taking information from me, Reliance responded that i should have called them directly and not the company listed on the service tag and as per their policy they would not cover this warranty service charge.

To add insult to injury, as a 'goodwill gesture', Reliance offered a $50 credit to offset this expense. What, if any, recourse do I have?.