Should I withdraw my paper because the editor is delaying the report? I am clearly disheartened by the editor's behaviour:

I sent a manuscript for peer review nearly three months back to an Elsevier journal with impact factor 0.625 in mathematics.

I inquired about the status of my manuscript after 1.5 months since it was still showing "With Editor " status.

The editor said review process is on and a decision can be obtained after 1 month.

After 1 month I again inquired about its status, to which the editor said that the report can be obtained in a few days.

But, since then, nearly 3 weeks have passed, but I did not get the report.
I have mailed the editor 2 times and the associate editor 1 time but no one replied.

The status is still showing With Editor.

Why is the editor behaving this way with me? I am waiting anxiously for my report as it matters a lot to me.

Are they avoiding my mails intentionally by not replying?

What is their aim? Do they want me to withdraw my paper? Should I withdraw my paper because the editor is behaving so badly with me?

NOTE: Also, if the editor is busy, why is the associate editor not replying?

My question is not a duplicate of submission review is taking too long because I never asked why my review process is taking long.

My question was 


  If the Editor said that I will get a report in a few days , why did he not keep his/her word and now when I am sending him mails, why is he/she not responding?


The two questions are clearly different as far as my knowledge goes.
The situation is sub-optimal, but not as bad as you seem to think. Remember that being an editor to a scientific journal, even one published by Elsevier, is often a volunteer job. Moreover, the editors have no control over how long the reviewers take to review your article. (which reminds me...) So what they gave you was only a guess. If the guess was wrong, then that happens. What seems to worry you the most was the status of your paper. I would not worry about that. Sometimes editors use these function to track submission and sometimes they don't. If they do, then the status is probably fairly accurate, if they don't then it means nothing. 

My suggestion is to think about publishing your article until you submit the article. After that you just forget about it (don't look at the journal website, don't think about it), because there is nothing you can do. Instead, focus on writing the next article. Only when you get your rejection letter, you start thinking about it again, and improve the paper and submit it to the next journal.