Sim Swap /Sim Inactive

I went to MTN branch in Maponya last month and their systems were offline so I managed to go back today and I was told that I can’t do a sim swap because my sim has been inactive for over 3 months, what I don’t understand is the fact that I use my number on another what’s app and I have been getting money transferred to the sim card but now it cant be re-activated. Can I please get help because I need my number and my money on that sim card how is it possible that a number is used daily on what’s app and monies are transferred into the number but now it’s in active and can’t be marked active. My cell no ***, firstly the number was ported to MTN and why should I be told that I will have to get a new number I don’t want a new number I want my number and money in the sim