Pin Numbers Changed

Morning. While trying to verify my credentials with the credit card division my pin was not accepted. I checked my profile on the FNB website and the pin had been changed....how is this possible as no one has access to my accounts. I tried to report this to the ***** division after the call centre put me through to them but they were unsure and I was put on hold.... wanted to check with the manager. I waited about 10 minutes then hang up. I want to put this on record in case anything happens.