How to respond to incorrect use of policy

I Have worked for this company for 4+ years now and have only had one "disiplinary action" Due to absences within my first year falling short of FMLA leave requirements.
I didn't fight it because it wasn't a huge deal.
But now as a manager I am on suspension for "improper use of employee discount"
I admited to allowing my father to use my discount with my knowledge not living with him. But they are saying that my boyfriend of 5 years and father to my children (a current unborn) I live with is also on the list of "cannot use" Because we aren't legally married.
But according to a previous employee that was fired for "improper use of employee discount" What she was told was as long as she was present for the use of discount there would be no issue but since she wasn't that's a violation.
I was present for the use of discount each time. Which is now why I'm getting into trouble.
So fact #1 I am being told what I did was wrong but another former employee was fired because she didn't do what I did.
Fact #2 the person who called in the complaint is a subordinate that is mad at me for not getting her all 7 days she requested off last minute. I got her 6 out of 7 and asked her to work day #7 and she agreed until after it was posted for two weeks. I know it was her because she left the hour after I was suspended going into another store and telling another coworker all about my situation with details she would only know if she called. Telling other employees about my "trouble" Getting suspended and hoping I would be fired.
Fact #3 I am only 5 weeks shy of being able to start my short term disability which is 12 weeks in total (if I take the entire amount of time) then 8 weeks of paid parental leave that just went into effect this last month 3/20/19.
So I need to know how to defend my position in these instances and be able to keep my job not to loose paid leave 6 months pregnant less than a month before applying for leave.