Another vote for Twitter, most supermarkets (and many other companies) have good customer service on there. I've had help from Asda and Tesco on there by direct messaging them. Usually pretty quick to reply to within the hours they reply.
Sometimes there is a bit of an automated service, Asda has one now so it guides you through to get the info they need to reply, like your order number, address, type of query. I just had a quick look and it asks for (relevant to your enquiry):
"Confirm your full name, address, email and Membership number (if you are one)
Attach a photo of the receipt, product, packaging (w/barcode, expiry date, supplier codes visible)".
Have you got a receipt you can attach? If not there should be an order number and you could always do a screenshot or the order and emails to save and attach.
https://twitter.com/coopuk/