Not release from project

Initially I am in RMG after that I have get 2 call from different project.

I gave interview in 2 project. I am selected for 2 project but in second project I am not interested to join, But they allocate me directly. But I want to release from this and join another.

I have received a notice from HR regarding the assignment to the abc project, but I am not interested in joining that project. I have been selected for a different project, and I would like to join that one instead.

But delivery manager said We are not releasing you.

What can I do? Please suggest.