Motherboard failure - inaccurate/false information from tech support

My Dell XPS 15 9570 just died. Sadly the warranty (one year) is over (1 year due) and the guarantee will cost me money (at least 100 EUR for the diagnostics).

Here is what I've done so far:

• unplugged the AC power brick and removed the battery
• plugged the AC power brick back in after waiting for a couple of minutes before trying to press the power button
• unplugged the AC power brick and used the battery only to see if something powers up

My notebook shows no sign of any life in terms of fans spinning, lights or noise. I checked the power brick via a digital multimeter and it shows 19.8V going into the notebook. I even checked the power rail where the DC In cable goes out of the power jack and into the motherboard. I also checked the power rail that goes into the battery (shows approx. 12V). I can keep checking here and there but I'm no expert so my inexperienced diagnosis is a failed motherboard.

I contacted the tech support of Dell and after almost 18min of waiting my call came through (I'm in Germany so I contacted the tech support in Germany). The lady told me that such failure is covered by the customer especially since the warranty has expired. For diagnostics (which is required before choosing what to do next) I have to pay 100 EUR or so. I am unwilling to do that and for now I will look into local services that can help me out.

What I found surprising and highly inaccurate or even untrue are two things I was told:

• After stating that I would like to replace the motherboard myself I asked much the part will cost (mind the fact that the motherboard has also the CPU and GPU on it, which unlike a desktop PC are very difficult to remove and put back on due to the way these are attached) and I was told 180 EUR. I asked multiple times (her German was not that good) and even exclaimed in surprise that it's so cheap. I checked on various websites including parts-people.com and for the part with number F3DC8, which she gave me, the price is around 600 USD, which will probably mean around 700 EUR given the deal most EU countries get on PC parts in general. So my question is how much does the part cost?!
• After that I told her that the diagnostics is too expensive and I would like to replace the motherboard myself. She told me that the part can be find in the online shop. Needless to say I made a comment here too that such parts are normally not found in the online shop of OEMs. She said that it is available. After the conversation was over I checked by entering the part number and of course no results were found.

Even her email, where she send me that part number, is confusing. I told her I don't want to use Dell's service due to costs, shipment and how long it would take for all that to go back and forth. In her mail she says that after the workshop diagnoses the problem (again - I DO NOT WANT TO USE THE DELL'S WORKSHOP!) I need to give the part number F3DC8.

I am now looking into contacting the repair workshop from there (the closest one to where I live in Germany) to see what the heck is going on. I found some information at https://www.dell.com/support/article/en-us/sln284409/so-veranlassen-sie-eine-reparatur-ihres-dell-systems-nach-ablauf-des-service but I am yet to find direct communication channel with them. I fear I need to call tech support again...I have the feeling such companies intentionally hire people, who barely speak the local language, just to avoid supporting their customers. Absolutely horrible attitude! I would get the motherboard failing right after purchase, which would indicate faulty part, but this is after the warranty has expired (how convenient) and in a machine that cost me 1600 EUR. If the motherboard indeed costs 600 EUR I would rather buy a second hand notebook than pay for this nonsense.