TELKOM NON EXISTING SERVICE

I TRIED TO HELP MY MOTHER TO GET HER LANDLINE MOVED FROM ONE ROOM TO ANOTHER IN THE SAME OLD AGE HOME. AFTER 5 MONTHS I'VE GIVEN UP AND AM CURRENTLY TRYING TO CANCEL THE TELEPHONE LINE BUT TO NO AVAIL. THE LAST TIME THEY KEPT ME ON THE LINE WHILE WAITING FOR A SUPERVISOR TO SPEAK TO FOR 48 MINUTES (ON MY CELLPHONE). WILTS WAITING ALMOST 20 MINUTES I CALLED "HELLO" INTO THE SPEAKER, THEY STARTED LAUGHING AT ME AND CLOSED THE LINE. AFTER THIS A LADY CALLED AND SAID THAT SHE WOULD SEND ME A FORM TO FILL IN FOR THE CANCELLATION. AFTER COMPLETING THE FORM I SEND IT BACK AND RECEIVED A MESSAGE "MAILBOX FULL" WHAT NOW?????