YOU SAID:

oh hi i didnt see a cat

INTO JAPANESE

ああ、こんにちは私は猫を見たdidnt

BACK INTO ENGLISH

Oh, hello I did not see the cat didnt

INTO JAPANESE

ああ、こんにちは私は猫がdidntを見なかった

BACK INTO ENGLISH

Oh, hello I did not see the cat didnt see

INTO JAPANESE

ああ、こんにちは私は見たことがない猫は見ていない

BACK INTO ENGLISH

Oh, Hello I have not seen a cat I have not seen

INTO JAPANESE

ああ、こんにちは私は見たことのない猫を見たことがありません

BACK INTO ENGLISH

Oh, hello I've never seen a cat I have not seen before.

INTO JAPANESE

ああ、こんにちは私は以前見たことがない猫を見たことがない。

BACK INTO ENGLISH

Oh, hello I've never seen a cat I have not seen before.