Threatening emails regarding payments no and reply and mails

I received a email from Supersonic whereby I was threatened with Legal action regarding an outstanding amount. This after I made arrangements via Email that i have proof of. I then went on and paid the full outstanding amount, send proof of payment and numerous email to confirm that the payment have been received and that the account is settled in full but to no avail. The persons that was in charge of the mail that was send was Sizwe Ndende, before i dealt with Vanessa Nkuma, I have now tried multiple times to get in contact with either of them via email, i can see that the mails are going through as om getting read Receipts and yet no feedback. I called the *** number numerous times- stayed on the lien for 20 min and longer with no answer from the accounts department. This is poor service. They are ignoring my emails, not getting through to supersonic just to confirm that all is in order payment have been received and to get a letter (As i do not trust supersonic and or their employees and their feedback) need it in black and and white on paper to say i do now owe them anything - this is a chapter in my life i just need to get over