Hi @Trench23,
It looks like the libertyglobal.com domain sets CAA records that indicate only GlobalSign is allowed to issue certificates for this domain. Let's Encrypt sees those CAA records and refuses to issue for the domain.
If you want to use a Let's Encrypt certificate you will have to update your CAA records. I recommend using SSLMate's CAA Record Generator. You'll need to add a record like:
unitymedia.biz. IN CAA 0 issue "letsencrypt.org".
Our CAA documentation page might help explain more.
Good luck!