I setup Email Service store/forward with my domain and it was working fine but I changed my mail server address so I changed MX record accordingly then everything stopped coming in and all my messages were returned.

I tried reverting everything and even changing ETRN port but nothing works.

Do you have mx1.dynu.com and mx2.dynu.com in your MX record? MX records are destinations for email for your domain name. They should not be removed.

I accidentally removed them when changing MX reocrds. No wonder it stopped working. Added them back and everything is ok now.