Is a seller still commited to sell an item if they underestimated the postage cost?

[twistingknickers]

I recently purchased this item # 350715133801 from the UK. I am based in Australia. As shown in the listing, the seller ships worldwide at £6.99.

Upon checkout to pay for the item, the shipping has now increased to £13.99. I messaged the seller to rectify this increased postage and was told that they were unaware shipping to Australia would cost so much and they would in fact make a huge "loss" on postage; and was given the option to cancel the transaction.

However, I do still want to go ahead with the purchase, but only at the postage the seller set themselves, not at a belated inflated cost.

The seller has noe opened a cancel transaction case for this item giving this reason:

"Seller comment: Unfortunately I made a mistake with postage cost and didn't realise the buyer was based in Australia. Apologies again."

I have not paid the item yet, but will as soon as the postage cost is corrected. Am I within my rights to not agree to the cancel case?