YOU SAID:

youve done this before haven't you

INTO JAPANESE

あなたはそうしなかった前にこれをやった

BACK INTO ENGLISH

You did this before you didn't

INTO JAPANESE

しなかった前にこれをしました

BACK INTO ENGLISH

Did this before did not

INTO JAPANESE

前にこれをしませんでした

BACK INTO ENGLISH

Did not do this before

INTO JAPANESE

前にこれをしなかった

BACK INTO ENGLISH

Did not do this before