Take "Cong" as the surname source, and say that it comes from Ji's surname. During the Zhou Dynasty, Zhou Gongdan's second son, Guan Bo, was sealed in the land of "slaves" and was called "slaves". Their descendants will take Cong as their surname.
As a surname, "Cong" is different from "Cong". It is said that during the Qianlong period of the Qing Dynasty, in order to maintain social stability, the emperor gave some Hui people surname Cong. Among them, the central doctrine of the ancestors belonging to Islam is "harmony and obedience", which is also one of the sources of subordination.
In a word, "cong" and "cong" can both be used as surnames, but their origins and historical and cultural backgrounds are different.