If you are forced to conclude that it is a scam then you shouldn't trust it and find another. It is also possible that you have joined a fake myNode telegram support because if it is the real telegram support channel then they wouldn't have asked for your private key. If you have time to make a fool out of them then you could try creating a dummy account and give them the private key and see what they will do. To be honest, a telegram support asking for private key is likely a scam and shouldn't waste your time on them if it's up to me.

If I am not wrong, is this the site that you have tried?. https://mynodebtc.com/. I checked the telegram support channel and this is what I found. Is this the telegram you have ask for support?.
https://t.me/mynode_btc

I think you might have been to a wrong telegram channel if I am not mistaken.