I have been praying Asr and Isha wrong my whole life :(

Recently came across to a video on insta a brother saying you probably make this mistake in salah. he said on the 3rd rakah of asr and isha's sunnah, i am suposed to recite subhanaka when i begin just like in 1st rakah and i had no idea. i went to quran course many times as a kid, i also went to islamic school both but i learnt this on that instagram reel. i have been praying them not knowing i have been doing it wrong. i am so shocked and sad because how come i did not know this... i told my sister about it and she said she had learnt it later as well. was i taught wrongly i wonder...