Q: Should I withdraw my paper if the status is showing "Editor invited" for several months?

You have mentioned that you submitted the manuscript on 07/12/2017. Did you mean that you submitted it in July 2017 or December 2016?

In case you have submitted it in December 2016, I think you should withdraw the paper immediately. If you have submitted it in July this year, I would still say that the journal is taking too long to process your paper. Ideally, the manuscript should be assigned to an editor within a week after submission. However, in your case, it has taken 40 days for the status to change to "Editor invited." In fact, this probably means that the Editor hasn't yet accepted the invitation, so your paper has still not been assigned to a Handling Editor.  Moreover, since the journal is not responding to your email, you don't even know by when you can expect to see a status change. I think you should send another email to the editor and if he/she still does not respond, you should consider withdrawing your manuscript. 

Recommended reading:

• How to write a withdrawal letter to the journal
• What can I do if the editor does not confirm my withdrawal request?
• What can I do if the journal is not responding since eight months?