Ignoring my email for my paid up letter

I made an arrangement with nudebt to pay my Telkom account, from the set go i paid my instalment which was divided into 4 months, they did not have to call me, i paid each monthly and when i finished paying i called for paid up letter which was promised to be sent, nothing and i called again and then was promised within 24 hours,i called after 72 hours and they hang up on me. I sent several emails and they just plain ignore them.

Very bad stinking service. Im not done untill i get this letter.