Can't guarantee that you didn't receive a scam call but, to try to offer some encouragement, if you have a look through the forums (such as 'Account Management - Cable') you will find dozens and dozens of topics from customers who have had conversations with VM's sales agents who promise X, Y and Z including call backs, confirmation letters and fantastic deals all of which frequently fail to materialise and VM then have no record of (particularly the fantastic deals which were agreed on the phone).
If you want to speak to 'retentions' I'd suggest (from recent personal experience) that you try dead on the dot of 08:00 when the lines first open. This will give you the best chance of getting through to a UK agent with least delay. When I called in this way, I was connected straight through (didn't get offered a fantastic deal though!)
If you are in doubt about your previous phone call, you could do the basics such as change your VM password, security question etc. just in case.