mtn's loophole

Hi everyone, My name is Tebogo Mokgosi From Pretoria, Capital park.i have a problem with mtn because i can call for free without using airtime or using the airtime of the receiver, any number as long as they have called me before. now the problem is i tried to reach out to mtn customer care to tell them what i can do with their network of which i tried with other networks turns out mtn is the only one with that loophole. so mtn doenst want to give me a chance personally prove that i can call without airtime since 2019 till now. they want me to tell them over the phone. imagine what should i do