Mtn
No final billing with antagonistic threats

I have been an MTN customer for 10 years now, and have moved from contract to prepaid.
i have not received a final billing, however received a threat that I need to pay the balance or else my account will be cut today.

I settled final payment, but now receiving these threats.
I am now not able to contact MTNSP as my account has been moved.

Please close this final "billing."