What can I do if seller changes handling time after the fact

[littlejaybird91]

I have recently bought an item using mobile ebay and double and triple checked all the delivery dates, handling time etc to ensure it would be here by the 25th before bidding. Nothing ever said anything about handling time other than that seller ships within one day of receiving payment. I didn't have a card to pay with so had no choice but to pay by echeque, which cleared Wednesday. I messaged the seller and got a reply that they won't be able to post until the 31st of August and claims that it was noted in payment instructions which never came up on my phone. I have just checked the listing again and cannot find anywhere where this is stated. Is there anything I can do about this as if I cannot receive the item by the 25th I need the funds before then to try and find another identical (or at least similar) item.