I believe what occurred here was what Amazon refers to as an ‘ASIN Merge’. First steps is to make this product ‘Inactive’ until fixed because you do not want to sell something that does not match what the product page is.
Since the original ASIN (B000XANK90) (UPC Code: 805676300719) does not exist and your inventory now shows a different ASIN (B004W95TA6) (UPC Code: 805676300986), this is the only logical answer.
An ASIN merge is performed when Amazon is notified, and believes, there are duplicate product pages. Since Amazon’s catalog is designed to have a single product page for each distinct product, Amazon will merge product pages. Sometime they are wrong and we need to engage Amazon to correct their error.
If this product page is/was not an exact match to the previous product page, you will need to open a case with Seller Support and request a ‘Merge or split product page’ be done. Basically your asking them to restore the previous product page and split this merge back to the way it was.
You will need to provide proof these products are different. Usually stating the UPC code differences and/or links to manufacturers website for each product will be the best evidence you can provide.
Also, you should have received an email from Amazon advising you of the merge (Subject: Amazon.com ASIN Merge Notification). It is standard practice that Amazon notify sellers of the page that is being deleted, so they can review to ensure a match. Did you not get such an email?