Money was deducted from my Debit Card even if I didn’t use it

Hi everyone, I need your help on the following problem

I bought some clothes from a shop with my MUFJ Debit Card, the initial total was 11,500 yen

But soon, I wanted to return one of the items and they paid my 11,500 yen back into my account and deducted 9700 yen.

This happened in a mall in Gunma Prefecture on 31st August.

Again on 4th of September, the same store deducted 11,500 yen from my account. Even though, I didn't purchase anything from the shop on that day.

I just MUFJ and they said that they can help me in blocking the Card or I could at first ask the shop via phone call tomorrow, since it's already late today.

I am panicking, so any help on what I should do, and how I should be careful will be very much appreciated.