My husband past away 4 years ago and I found out that he had a some shares from a simple IRA w/ his job.?

Im the wife, but I was not listed as the primary beneficiary, so I was told that I cant redeem benefits. When I first called this company, they told me that because I was the wife, I was owed this money. Later, I get a letter in the mail saying that his mom was listed as the primary beneficiary, and I can only get this money if she allows me too, in so many words. Is there anyway possible that I can overide this and still redeem the funds? I feel cheated, as a wife! lol