I'm 62 and received a check from social security when my mother passed away why is it being treated like it's a payment for my social security?

If you received a social security benefit that would have been payable to your mother and/or the one time death benefit, you would be responsible for paying the income tax on it.  If you did not receive it, you should contact the Social Security Administration immediately.  If you want to send the payments back, you will not have to pay the tax.  

"why is it being treated like it's a payment for my social security?"

Because that's the way it's supposed to be treated.  A Social Security payment made to you is to be treated the same whether it's your own Social Security benefit or it is paid to you as beneficiary of your mother.