Speaking to Fin24, the bank's CEO, Gerrie Fourie, said 2000 accounts had been closed to protect its clients. Some of the clients, however, reacted so aggressively that the bank had to bring in security.
MMM SA is part of MMM Global, which is linked to Russian Sergey Mavrodi, who in the 1990s was involved in one of the largest pyramid schemes ever.
He was jailed for his involvement in the scheme.
Hawks spokesman Brigadier Hangwani Mulaudzi said the elite police unit was investigating MMM SA to establish whether it was a Ponzi scheme.
Actuarial Society of SA CEO Mike McDougall said: " It can be stated with absolute certainty that these schemes will eventually collapse, leaving many people financially destitute, while only the founders and a few early participants make considerable gains ." - The Times