If you click on the listing from your purchase history, there will be a note at the top that says something like "the seller has revised this listing, but you can view the item you purchased", that will contain a link to the listing exactly as it was at the time of your purchase. (At least, you can do this on a PC, not sure what happens on the app).
If the original listing definitely shows it as intestinal wormer, then it sounds a bit like the seller did it deliberately given their response (they may have made a mistake in the original listing and thought this was a better solution, or ran out of stock so could only send the other product, either way if it was intentional it's a poor way to handle it). I'm guessing the seller doesn't realise a record of the listing you purchased from is kept by eBay for around 60 days, but at least you can show them undeniable proof that refutes their claims (the revision history of the listing is also clearly shown - it will say the exact date and time changes were made, and what those changes were).
