Data transfer from my current iPhone

I really regret having bought the new iPhone 12! I tried to do the data transfer from my current iPhone 6s 4 times already, 3 times with the apple support hotline and 1 time with the local apple dealer. all attempts failed ... you buy a premium product and expect it's working, but you need to invest hours and hours to find out it's not! such an embarrassing experience! if I could, I would immediately return the new iPhone and not buy any other one!

[Re-Titled by Moderator]