Nasty tactics by ex employer

After being forced to leave my job due to being bullied and the employer not wanting to "get involved" alot of nastiness has ensued. I am now being accused of being Fraudlent by the employer because of this....
When I was first appointed as manager it was discussed that when staff made purchases they didn't have to pay the extra markup ie:
wholesale cost = $55.00 standard markup is $55.00 x 2 + 10% GST = $121.00. That would then be put through with an extra markup at $150.00. When a employee purchased goods, the extra $29.00 would be deducted before taking off the standard 25% discount for all staff including myself.
Now the employer is taking the position that it was unauthorized and fraudulent.
She has also charged clothes to my account that were gifted to me (every staff member recieved gifts but only mine have now been charged to me) and in a letter stating that I took them from the shop while she was away without her permission.
She doesn't mention I left the price tags on her desk with my name on them as she requested. On top of all this, she has now started charging late fee's on my account out of spite. We never agreed in writing or verbally that there would be any late fee's or admin fee's.
Unfortunately for me, she has the support of the staff, as they were the ones I resigned over.
Where do I stand in this matter. She has even gone as far as contacting my new employers and telling them lies about me. In this case it hasn't helped her as she has defamed them on previous occasions.
I am sorry for the written saga...but I am desperate for some advise.