Not exactly the company you want to work with if y...

Not exactly the company you want to work with if you are living abroad. Their requirements for residence documentation are more difficult than banks etc.

In my last request, they even wanted me to send them a "selfie" :)

Not a company I can recommend.

I have moved to another provider already, who seems to have order in their documentation requests.

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Comments to your answer below;
HMRC, Companies House, and my UK Bank accept the same documents I sent you, with no comments.

I have been customer at your company from 2015. When I added a new company, then you ask me to provide "selfie" and get my documents notarized at a cost of 200 euro extra, just to satisfy your own "rules" / or maybe your misinterpretation of the given law.. this is for no use as the organizations mentioned above did accept the documents without any comments.

It seems like your company are not fully equipped for international customers and your requests on getting foreign government documents notarized just add distrust/suspicion on your customers.

Further, using your answer below as a advertising for how good and professional your company is and that you just are following know your customer rules, is at least a bit ironic, as I have been a customer at your company for 5 years, and you did not recognize that (know your customer).