The youths - the youngest of whom was a 13-year-old girl - died in June while partying in a popular nightspot in a township outside the coastal city of East London, Eastern Cape province, and the grieving relatives had been demanding answers.
A health department spokesperson for the Eastern Cape province declined to comment on the results of the investigation and told reporters the probe would not be published.
Multiple causes for the death of the teens had been flagged in past weeks, including poisoning from what they may have eaten or drunk.
"The report has come out but I'm not happy about it," said Xolile Malangeni, whose 17-year-old girl, Esinako, was among the victims.
Xolile and others complained that the results were communicated by the authorities to them verbally.
It is unclear what caused the youths to suffocate.
Local news TV eNCA reported on Thursday that asphyxiation had been caused by overcrowding.
In June, a source close to the investigation told Reuters the young people may have died by poisoning from a gas leak .
The owner of the bar has been arrested, charged with supplying minors with alcohol.
