Impossible to cancel MTN

Hi, I want to cancel, but remain as a pre-paid client (retain the number - to do with what I want; port perhaps, remain a prepaid mtn client...etc). I stand in a long que in Bayside centre. In front I am told I can only cancel by calling 808. I do. Lively music plays. You must choose an option - whether to upgrade or cancel. I do. It keeps ringing for 20 minutes. Lively music plays. I call again; choose the option to upgrade. The music is slow, calming. The call is answered. I say: Hi, I want to cancel, but remain as a pre-paid client . She says: Hold on for retentions. I do. The same upbeat music plays. I hold on. I join the que of another company. I end up in front. I take out another cellphone contract. The MTN cancellation line still rings. On my way out I report this to MTN. They phone from my phone. It just rings. How now??? My suggestion so far - Don't join.