If i understand correct, you have been paid more than you should receive? Right?
If this is the case you are overwhelmed with, you can simply send back the amount to the address you recieved it from
That's the worst thing you can do! Never send back to the same address that you've got the money from without confirming it with the other party. They may not be in control of that address anymore and the money will be gone forever, which would be a waste since it's a huge sum.
You already did what you were supposed to do. Contacted them via all available means and got no answer. Hold the funds for a while, maybe a week or 2 from now they will find out they're missing some money and contact you or they will find your messages and respond. If not, feel free to spend the money.
I'd wait a month or 2 and then treat it like a gift.
or donate it to my address BTC 32FS9mC6BPFMm57p7fAH2ubg83awPeCq7V
That's even worse than your previous idea.