Invoice errors

[amazing*finds*2016]

I saw a listing with something I wanted.  I emailed the Seller and asked if I bought 3, would she combine shipping.  She said sure, it would be $4.00.  So, I put the items in my cart and sent a request for an invoice, therefore committing to buy the items.  The Seller sent back an invoice with not only the original shipping of $8.70 for all three, but an added shipping fee of $4.40.  She will not respond to my messages and when I tried to contact eBay, they gave me this outlet only.  What should I do now?