Irs is keeping my return. Been trying to resolve this issue with them but can’t get through to them via phone or mail

Not much you can do about that ... have they sent the letter of explanation yet telling you why ?  

"can’t get through to them via phone or mail"

I'll tell you how to reach a live IRS agent below.   If you can't get good answers from the IRS, I'll also be telling you below how to contact the IRS Taxpayer Advocate Service.

Is there any clue as to why your Federal refund was withheld?   Was there an offset?  Any message here:
https://www.irs.gov/Refunds

Here's how to reach a live agent at the IRS:

800-829-1040 (7AM-7 PM local time)

When calling the IRS do not choose the first choice re: "Refund", or it will send you to an automated phone line.

• First choose your language.  Then listen to each menu before making the selection.
• Then press 2 for "personal income tax".
• Then press 1 for "form, tax history, or payment".  
• Then press 3 "for all other questions."
• Then press 2 "for all other questions." 
• It might transfer you to an agent at that point.   If it doesn't it may ask for your SSN, but do not enter it.  Just wait.    If it asks for SSN a second time, still do not enter it.
• Then you'll get another menu.  Choose 2 for "personal" then you should be transferred.

I usually use a speakerphone so I can work on something else while waiting.

If you don't get good info/results from the IRS, you can contact the IRS Taxpayer Advocate for your area.   They are especially prone to help if you have a hardship, or if there have been continued delays with lack of info from the IRS.    At the following IRS website, find the USA map and click on your state, and it will give you the number of your IRS Taxpayer Advocate.

http://www.irs.gov/uac/Contact-a-Local-Taxpayer-Advocate

Also see this article for more info on how the IRS Taxpayer Advocate Service works::
http://www.irs.gov/taxtopics/tc104.html