Ebay software will not let a seller change a listing in any way once the listing is closed so I seriously doubt the seller changed it.
There have been reports in the past of items being shown on the phone app incorrectly with free shipping while viewing the item on a computer shows the correct shipping charge. Perhaps that is what you are seeing? What was the listing number?
At this point all you can do is message the seller and ask him to cancel the sale. The seller is not required to but he may anyway. If he doesn't cancel your choices are to either pay anyway or else not pay and take the non-payer strike on your account.
