I tried *141# but it only shows my normal balance, I've just purchased a 1 day uncapped to give it a try. USSD code *141# doesn't show the uncapped balance.
OK so it took them (MTN) about three to five minutes to sent the SMS Y'ello! You've successfully loaded a MTN 1 Day Internet Bundle. Please dial *141*5# to activate your Internet Bundle. See www.mtn.co.za for Ts and Cs