Complex sentence: During the last week of August, the song dropped to number 59 and in the first week of September the song was still on the charts at number 54 in which the song had already spent 17 weeks on the charts.
Split into simpler sentences: During the last week of August, the song dropped to number 59. In the first week of September the song was still on the charts at number 54 after 17 weeks on the charts.