How to tell a vendor I'm not in need of their services anymore?

Soooo recently I posted about my musicians that I hired. Long story short, I thought I was getting my violinist and cellist duet, but unfortunately they changed that on us and will be providing a flutist and cellist duet instead. It wasn't under their control and something happened to their 2 violinist backups. I was pretty disappointed hearing the news because my heart was set on a violinist and cellist, and that's what we first initially hired them for. I know a flutist would sound just as beautiful, but everytime I look up YouTube videos of flutists and cellists together, it just wasn't the sound I wanted...


So then I reached out to other musician companies in my area just to see what's available and I found someone last minute that will provide a violinist and cellist duet!

Now I'm wondering how to break the news with my current musicians? I've only paid for the non-refundable deposit so not much will be lost. What should I tell them? Say "unfortunately we are no longer need of your services" ? Would I have to give a reason why? How should I word it? I also feel kinda bad doing this to them. 😔 Help!