Q: What should I do if my paper has been under review since 5 months and the journal is unresponsive?

While delays in peer review are not uncommon, 5 months is quite a long time. Additionally, the fact that the journal is not reponding to your emails is somewhat worrying. I think you should send another inquiry to the journal. Keep following up every week till you get a reply. If you don't get a response even after sending 4-5 emails, you can consider withdrawing your paper.

Related reading:

• What to do in case of delay at the journal end and no response from the editor?
• How to write a withdrawal letter to the journal