Pi-hole+unbound Set DNS

I’m not 100% sure but these might be two different thinks. Unbound is doing DNS resolution on a first step and this should be working. What might be done by the ISP is to prevent the client access to the web site at the end. But as said, I’m not 100% sure how DPI is working on your ISP.

There isn’t really any way around this, except for using a VPN (obviously the VPN provider can still perform DPI if they wish, so choose a provider who handles user data in a way you are comfortable with) or using the Tor network.