if the transaction has been confirmed the block is declared to be a valid transaction.
but that makes it difficult for our funds to return we have to know the owner of the bitcoin address (here is the most difficult point)
What would you do if a clipboard virus is injected in your PC and you copy some address but the virus changes the address in the clipboard with the one it is intended to send to? Is it your fault or Bitcoin's? It's definitely yours because you aren't mature enough to check the address and then send everything in a hurry. I mean, what the hell? Why do you guys don't do a double check before sending BTC to any address?
Let me.shoe you an example which is one of some mistakes I encountered (but thank God I checked it and didn't withdrew my coins from the exchange):
I used Brave browser to use my VPN and login to the exchange.
Then, went to "withdraw" section and decided to take my coins out. Then copied the address of my wallet which was a legacy address and pasted it in the withdrawal address box.
Then, suddenly the fear of paying higher fee while spending my coins from a legacy address struck my mind (yeah, I know not much fee now but I'm talking about the time when fees were above 20k SATs for instant confirmations) and I decided to use a SegWit address instead starting with 3.
I copied it from the same wallet and then tried to paste it in the withdrawal address box, but when I tapped "paste", it pasted the legacy address once again instead of the SegWit one which means that the clipboard in Brave didn't update while, when I tried to paste it in other apps, it worked fine. Then I opened a new tab in Brave browser and pasted it in the address bar and SegWit address was pasted there, I copied it from the address bar and then pasted it in the withdrawal box and voila, it worked! But this shows that you need to be very much aware of the possibilities because it's not just limited to viruses and hacks, sometimes your least stupidity becomes your worst enemy to make you lose your everything.
Additionally, Mycelium allows you to stop your transaction from getting broadcasted (only if you're lucky enough while the transaction fails to broadcast). You can cancel the "already done" transaction (read my words two times, "already done" doesn't mean "already sent") if it was not broadcasted to the network and failed, but there's a small line worth of a chance with least odds of something happening like that.