Amex. continued charges without ability to use services.

I initiated my Amex card some 25+ years ago whilst travelling abroad extensively and Amex was a great way to go. Things changed and I have not used my Amex card, nor had one since 2008. I have attempted to terminate there services without success and whilst there charges have been minimal =/-R50 this continues to be debited to my account on a monthly basis. My last letter to Amex after my communicating with there call center ref. 35697252 ( as they would not assist me telephonically) remains unanswered (besides system generated receipt). I have had no card therefor unable to use service and continue to be debited, even after the last mail. After phoning and e-mailing what further can one do? Obviously the discrediting of there name means zero as a large corporate will laugh off such a trivial matter with disdain towards the customer. Naturally, and whilst taking legal action over principal is an expensive alternative same seems to be the only way forward to resolve this matter and/or via the Ombudsman and waste their time? Nedbank spend many millions of advertising in an hugely competitive marketplace, and I enjoy their adds, however how would I ever contemplate moving from FNB/RMB Private and Standard bank given the above.