Punitive, Unfair and Scrupulous Admin system

I made an arrangement to pay my overdue account. I have been paying this account regularly since October 2017 to date. I called in several times to request a letter that confirms this arrangment. Each time i call in, i am told i must must paid in succession 6 months. i have done this. my frustration is, i get told my payments dont reflect in their account by the 1st monthly ans therefore it cancels the arrangement. i find this unfair and punitive. i have no away of controlling inter banks transfers. now i am told by Nonhlanhla who has put me on hold for 21 minutes that there is nothing she can do and her manager has gone home. I need this fixed urgently as my life and credit profile is impacted by this tardiness.