MTN sim swap horror

I lost my phone on the 22nd Sept, I called MTN the next day to do a sim swap and block the phone. 5 days later the sim swap has not been done and MTN has allowed the person who stole my phone to use my sim card and access my cellphone banking even after I reported to them that the phone and sim card have been ******. The person who stole my phone has bought R 780 airtime and I believe they probably selling it, but MTN refuses to conduct an investigation on this.