Why does Xfinity Mobile block Port 53?

I wanted to stay safe on the internet so I purchased a great VPN. I wanted to avoid phishing, malware and hackers. But who knew Xfinity Mobile would block Port 53? Is this a privacy policy problem? I need my VPN to stay safe on the internet. 

Blocking my VPN so you can use my privacy and I can't stay safe. How's that work?