Just checked my emails and the first thing I see is a fraud alert from Amex saying they stopped a £87 purchase from Just Eats last night on my account. The email had two buttons to confirm if the transaction was authorised by me, or not. Being usually suspicious of email links, I directly called the Amex fraud number (0800 077 8057) which I had in my address book from another fraud alert many years ago. After the usual identity checks, the Amex lady confirmed the email was genuine, has blocked the card and is issuing a new one. She also said that they have seen a spike in such transactions recently which is why they declined the payment; another reason for blocking was it didn't fit the usual pattern on the account.
Just thought I will share this, especially the direct number, in case any one else has a problem.