Yes I have had a similar problem, but it was resolved immediately. I and another woman bought fabric, the packages got mixed on shipping and we received each others items. The seller contacted both of us asking if we would be willing to swap packages by directly shipping to each other and seller would refund shipping cost to us. We both did and everything ended happily.
The seller you are working with is trying to pull a fast one. I have been buying and selling on EBay for years and I work very hard to make sure I do as much as possible to please the customer.
Greed is running the show with this woman and she needs to be reported. Sellers like her ruin it for others.