No miles?

I am a frequent flyer and have been a loyal SAA client for years. I have never redeemed by points. I diligently add my points either using the self-service box at the airport or a regular counter. I have always received a 'successfully updated' message and have been assured by counter staff that my miles have been allocated. Upon attempting to redeem these miles I was informed that I do not have a single mile allocated! To add insult to injury I was also informed that in fact I cannot redeem miles further than 3 months ago? What has happened to my miles?