Bad service for debit order

In October 2017 I changed my bank accounts from ABSA to FNB. That very day I went to telkom store in capegate shopping center cape Town to change my banking details. In December I noticed that my debit orders for the telkom account did not go off. I then went in to the store again to change details with Bank statement. In January no debit order went of again. In February 2018 I went in to store again to change banking details and in March 2018 no debit order again. No in April I received a SMS from nudebt that I've been handed over for debt collection. Why Telkom, I've done my part but due to your staff not being able to do theirs you want to hand me over for debt collection. Bad service. Done with you guys.