VMG8623-TS0B login problem

I received it brand-new, unopened in box, from someone and I cannot get into the configurator. The USERNAME - LOGIN PASSWORD that is printed at the back of it, simply does not work. The Wifi name-password works, but the login details for the configurator do not. Before you say it, I did hard-reset the unit several times, with no luck. Tried admin/1234 and it didn't work either. Did they somehow print the wrong details at the back of the router, or what? Or did the local ISP mod the firmware and it somehow affected this? And how do I get around this? Are there any login details that work in these cases? Returning to sender is not an option, as I received it, didn't buy it.

Details for this are:

User name: admin

Login password: K7GBKJPH

Serial number: S210Y24025821

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