YOU SAID:

I heard their sales have gone downhill

INTO JAPANESE

彼らの売り上げは落ち込んだと聞いた

BACK INTO ENGLISH

I heard that their sales were down

INTO JAPANESE

彼らの売り上げが落ちたと聞きました

BACK INTO ENGLISH

I heard that their sales fell

INTO JAPANESE

彼らの売り上げが落ちたと聞いた

BACK INTO ENGLISH

I heard that their sales fell