MTN South Africa

My wife bought a MTN Phone and uses it to phone my daughter also using an MTN phone but is charged as if she is phoning a non MTN Number. She has lodged complaints to MTN customer care on 18 May 2019 but nothing happened. When phoning the call center the staff are rude and not at all help full. MTN is terrible with customer service. Nobody seems willing to help us with our problem.