British Airways AVIOS Executive Club - trying to make a booking on this LOYALTY program is impossible!!

good day. i am based in johannesburg , south africa. i have been trying to contact the BA EXECUTIVE CLUB , to make a booking using my AVIOS. . i have been kept on hold for hours , trying to get through to someone to make the booking. i cannot make the booking on-line , as all the dates requested show unavailable!! i have tried all the phone numbers listed on directory enquiroes , in South Africa , on your web-portal, , at cape town international airport , but to NO AVAIL. Can someone call mje to assist. ?? i used to go into your ROSEBANK JOHANNESBURG OFFICES , and they were GREAT!! do you have a walk-in office in JOHANNESBURG. please adviose urgently. many thanks , what is the use of having a LOYALTY PROGRAM , if it is unaccessable / UNUSEABLE??