It’s a targeted Vodafone Select offer. To opt out, text STOP to 8586.
You’ve probably been targeted because of another piece of info you’ve given to someone. Could be insurance company database, could be something else. Have you used the Vodafone Select app? If you’ve ever entered a marketing survey or ticked a “share my info for offers” box where you’ve mentioned BMW that will be stored somewhere. Do you read all the small print/T&Cs on all web forms/contracts?
It won’t be because you looked at a for sale advert on here. Phone companies do have records of browsing from a mobile phone (legally they have to, plus for customer care questions when people want to know how they used their data) but only top level domain (and maybe after the first /, so singletrackworld.com/forum would be logged but nothing more).
(I’ve been involved with this as part of my job)