Unable to adhere to customer requests

Last year December I had requested that my account be changed from a cash account to a debit order. Spoke to an agent and was advised that this would have been loaded on the 25th December. First week of Jan and I receive a letter from Vodacom threatening to take up legal action for an unpaid amount. If the call center agent was competent enough to do there jobs I wouldn't have received that letter. Now this reflects negatively on my profile.