Make sure everything is in writing/email. Lack of a paper trail working something like this is a must. People have the natural feeling to pass the buck and let someone else handle it.
I’ve always found people/companies are willing to help and do what’s right if given a chance. I’ve found that with very few exceptions. Just document everything and be as nice and reasonable as you can be. I’ve seen too many become ugly Americans and lose the very thing they wanted. Firm can be most understandable, angry can go the other way. And that includes bad language, lot of folks won’t stand for that!