Sheer incompetence

In April we ran through a list of things to do before the move in June. So we try to cancel Telkom. Phoning got us nowhere, because they just do not answer. Ironic for a telecommunications company isn't it? Then we mail them April 21st. Of course, they ignore us and we get no confirmation. Having no luck getting a response, we go off to Bayside where we personally deal with a lady staff member. This lady confirms the mail of 21 April and we get given a reference with the date of our visit being 2 May. As true as Bob, we now get hounded again and again by Telkom telling us we owe them money for June 2015. Now please explain to me, how do you deduce that when we cancelled your service 21 April already?