How about being caught by immigration in South Africa?

Depends on why you were arrested by immigration. If the visa is invalid and hacked, it will be sent to the immigration court for trial by the immigration bureau. In most cases, it is repatriation and imprisonment, mainly depending on whether legal aid can keep up, and the most important thing is the severity of expiration. Very few people get away with it. Most of them were repatriated after the expiration. The good news is that in most cases, they don't have to buy their own air tickets.