Help. Current guest is angry they can’t extend because it got booked.

What do I do here? It’s as the title says. I gave a HUGE discount for the month (we do only 31+ days)because I felt bad for the family. They have been good guests, communicative and we’ve resolved any issues quickly as they’ve arisen. They say they planned on extending but here we are at the end of the month and another family has made an instant booking online for the rest of the year for full price. I let the current guest know so they can plan and now they’re angry, asking why I can’t reject the other guests and saying they didn’t make any complaints (about the issues we promptly resolved) because they wanted to stay. I’ve tried to explain politely how this works, how it is not a lease, etc. Now I’m afraid of any retaliation and/or a bad review when we literally just had the guest from hell before this one. Thoughts? Advice?