Harassment

I fail to understand how truworths clothing operates,my installment due for end of July was R130 and it happened that i was short of R30 i paid R100 now they are harassing me that im overdue with R160 how possible bcz its not end of august as in yet and i know i paid short amount and i will definitely pay R160 instead of R130 by month rnd why am i being harassed?being contacted by cellphone numbers?(+27 (81) ***) is that even professional ,this is one of the reasons why I closed their account previously I don’t deal with *** I know exactly that the installment i paid was short of R30 and i will pay my balance due and close the ****en account I don’t appreciate their service at all ,i feel like they don’t understand that they are dealing with human beings and not animal. The worst part i never received my card from them till now.