The best way to deal with this is through in-app chat (although this hasn’t actually worked for me either), as there is a flag that can be applied to make the merchant somehow “special” so that it doesn’t get constantly overwritten by people submitting merchant data.
The example I have is for Roadchef service stations. They all use UPay and have exactly the same merchant data, which unfortunately means that for almost everyone, when they look at the transaction in monzo it is in the wrong location. This leads to them submitting updated data, which COps dutifully change, not realising they’re just perpetuating the problem. I see a different location nearly every time I open one particular item in my feed…