Nedbank Credit card not honouring credit limits

1. How is it that Nedbank Card division does not honour the credit limit contract that we have? I have a credit card that is used by some-one else and the limit is contracted to be Rx. The user goes beyond the limit which by then they (Nedbank) should have declined. By the time it is 25% over the limit they contact me and ask me when I am going to pay in the difference. I then inform the consultant that I cannot understand that the limit is not implemented and get the normal SA answer being "sorry". I clean up the total amount of the card each month and I consider myself to be a model client. Why must I stick to a contract but they dont? It is a matter of setting a limit on the system, easy!!! 2. I keep on getting offers for ridiculous amounts of money/credit/loans which I as a pensioner dont want. If this happened once I would not complain but it seems to be impossible to get them to stop both these practices. 3. I am for what I consider to be a "private client" as it is thus indicated on my cards. When I contact "my banker" I am informed that I am not a private bank client. Why am I then getting cards stating differently? When I discuss it with the banker it still does not get fixed.