Here is a thing about OpenDNS you might not know. It actually has parental control feature that let you filter various domains based on category. They implemented by allowing you to enter your current IP address, and then all DNS requests from that IP address will run through the selected filter: https://signup.opendns.com/homefree/
One more thing. Mobile carrier often use CGNAT, which will put a bunch of customer behind the same set of public IP address. When you're behind a CGNAT, your request will appear to come from the same IP address like other customers of the same mobile carrier in that area.
What happened to you is someone in the same CGNAT enabled parental control on OpenDNS and registered the CGNAT's public IP address as their own. This result in everyone in the same network to have their DNS requests filtered according to that user's parental control settings.
You might need to wait until you got rotated into a new public IP address, or use a VPN. The real question is why your carrier use opendns in the first place.