New MTN SIM being processed for RICA registration for over 72 hours

My new MTN sim card has been processed for RICA registration for over 72 hours. I did a successful RICA registration in store and ported my number from a Cell C sim card. After my old Cell C sim card stopped working I inserted the MTN card for the first time and dialled *136# and got the error "Connection problem or invalid MMI code". I followed all the steps I was given, please assist!