Complex sentence: The song went to number one on the US disco chart, becoming the last single to hit the top spot during the 1970s, but did not reach either the US Billboard Hot 100 or "Billboard" R&B chart.
Split into simpler sentences: The song went to number one on the US disco chart, becoming the last single to hit the top spot during the 1970s. It did not make it on to either the US Billboard Hot 100 or "Billboard" R&B chart.