I extricated myself from being an Amazon Prime customer but recently had a phone call saying that if I didn't press 6 on my phone keypad I would be signed up again. Call ignored - but how did the caller know, or was it simply a guess?
A friend became involved in considering buying bitcoins and ended up with a demand for £1500 or of being reported to his employer for private work on his firm's computer and in their time. Ignored and he reported it to the firm's IT dept and it was sorted out.
I thought you had a BT 8610 blocker phone Danny - google unfamiliar numbers, there are several "who dialled me" sites which you can then block if dodgy.
Unfortunately they keep changing the number. I had 4 in one day about my non-existent Amazon Prime account and they were all from different numbers. Even so, I do block them.
I resent Amazon and others of like ilk because they are effectively not paying their fair share of tax. It doesn't always cost more to avoid them. Use Wordery for books, for example.
However, there are other means by which CC details can be obtained. Watching its use on a keypad, for example or buying something over the phone, and the employee stealing the security number.
I know they are paying the legally required amount but this is only because they are able to take clever advantage of tax rules. This means that competitors, hence UK citizens, have to bear the cost of providing all the services which Amazon and their employees need and want.