i request the package to be cancelled but its not

on the 4th of may i paid a month in advance for april to may and from may to the 11th june R1026. i cancel my internet on the 19th may, but i receive a bill at the end of june showing i must pay for the internet bundle from the 12 june to 11 july. i waited my one month for cancellation so it supposed to be cancelled off on the 19th on june why am i paying till july.. i called 10210 waited half hour after two agents answered and dropped the calls i managed to get through, the agent i got through was confused out of her mind, so she put me through to retentions after another half hour a agent comes on the line. i explain the situation to her. she did not understand why i am being billed for july when it shows on the system that its completely cancelled on the 19th june because i called to cancel on the 19th may. So she calls a billing agent name pinky ntombela, she says that it is cancelled on the 19th june but because they cant put such little days on the statement they bill me for the whole month and will credit me next month. why would i need to pay for a service i will not use, why is it not cancelled. Telkom has not been a good experience from start next step is the NCC.