No, I am not affiliated with Revolut, but there are many of these posts around the forum and I wanted to provide my experience with the required procedures.
To anyone wondering how to complain here is a guide to not waste precious time. If for example this is a chargeback complaint, or a complaint about a blocked account.
0 - Always first try your best to resolve the issue with the merchant if relevant.
1 - File a chargeback complaint with customer support if it is a chargeback. Wait the 45 days that it takes.
2 - If after that time frame Revolut “forgets” to inform you that they cancelled the complaint (as they are certainly bound to); or if the original complaint turned out dissatisfactory — then immediately write a formal complaint to email@example.com.
Bear in mind that the UK Financial Ombudsman will not help you if you do not follow its bureaucratic procedures, which means you will need to first file a formal complaint with Revolut at the aforementioned email address.
In general I would say that it does not really help to contact customer support to resolve anything other than some few basic issues. Just bypass CS and immediately file formal complaints when it concerns more advanced stuff such as blocked accounts, etc.
You must allow Revolut at most eight weeks to respond to your formal complaint according to the official advice of the UK Financial Ombudsman. Remember also to save evidence that you filed the complaint. This includes any auto-responses that the complaint was received.
3 - If at that point Revolut still did not respond to your complaint, or if the decision was unsatisfactory, then and only then you may choose to file a complaint with the UK Ombudsman office. This could take a year or more. Here: https://www.financial-ombudsman.org.uk/contact-us/complain-online
4 - Remember that, at any point, it is always possible to start litigation if the issue is very serious, such as large sums on blocked accounts. It can be very costly though. If you have proper insurance, then some legal costs may be covered.