Cards declined despite funds available!! No valid reason offered.

Both my wife's and my Debit cards have been declined on numerous occasions in the past year despite funds being available. I am a Private Bank account holder which counts for zip and the response to this over the last year has been appalling from my Private Bankers and Standard Bank. No urgency no valid reason and occasionally an apology. I am so done with this bank! I could write a book and yet the top brass stay away and send boys in to do a mans job.