That's because of your hidden MMR. You've been playing for a while probably so you've got your weeks of learning the game so that drags your MMR down so when you make a new account after having all this experience you place higher
If you cannot get out of bronze/silver on your own its very likely you will drop on your smurf to a similar sr over time. But use this time to learn and get better.
Also when people ask you if you are a smurf and what your main rank is either dont answer or lie and say its about the same as your smurf