What to do when a manuscript is still under review after 14 months? withdraw? I have submitted a manuscript to a journal, but after 14 months they have not given me any answer while I have sent email to them many times. Now, What can I do?

(I only received  a revision 12 months ago, and after I sent the revise version of the manuscript, I have not received any response. Also, a mailed them many times to everyone who I can find his/her email,  but no response. It's current status is under review.)
I was an ejournal senior editor for four years. Although few of them are really professionally acceptable, there are numerous confounding factors that can cause a break between an editor and authors. These include unanticipatable reviewer declines, lingering sponsoring institution policy changes including threatened journal cancellations, journal management system breakdowns, and of course, gross editor mismanagement.  A submitting author should hold a journal to a published timeline (including any extensions the editor requests and the author formally accepts) and withdraw their manuscript quickly for resubmission elsewhere if that timeline or negotiated extensions) isn't being met. This withdrawal should be written (electronically is fine) with copies to the Journal editor AND the Department Head of the sponsoring department/institution. An acknowledgement from either is to be welcomed but not necessary to terminate the relationship and allow the author to move on. When resubmitting elsewhere, an author may be requested to submit evidence of previous submission termination. I only made this request once (out of 300 manuscript submissions) and it was willingly supplied.