3D Secure’s merchant enrichment is effectively just a saved list of where the tokens got used after verification. It’s about the best we can do given the limitations of the protocol and data we receive. 
If you send me a direct message on this forum with the email address you use to login to Monzo, I can get the merchant ID for this payment processor excluded from enrichment matches. 
It’s worth noting that by the standard, payment processors should register a new merchant ID for every single merchant using their service but unfortunately, this doesn’t seem to be the case here.