MTN ?????

My husband passed away September 2023. I went to MTN and gave them all the necessary documents... 3 times. Then I got an email after 6 months stating he is in arrears with R3000+. I went to MTN again and told them what happened. I was then told that they will do the necessary! Last week (almost a year later....nothing in between!) I received a letter from NUDEBT stating that late mr Visser must pay his account asap!!! Who is doing what wrong?????