An ICO spokesperson said:

“People have the right to object to their personal information being used for direct marketing, and we have been clear that online targeted advertising should be considered as direct marketing. 
 
“Organisations must respect people’s choices about how their data is used. This means giving users a clear way to opt out of their data being used in this way. 
 
“If people believe that an organisation is not complying with their request to stop processing their data, they can file a complaint to us. We will continue to engage with Meta on this issue.”