Paying in installments

I have arranged with Lancet a couple of months ago to pay off the amount owed in installments. But I constantly received e-mails and sms notices stating I have not paid. I am already stressed out about money since I unfortunately am under Debt Review. To receive these messages the whole time only adds to the stress. And to receive it in the middle of the month when there is NO money? Why not send the message after the day I said I will pay, or after any normal person receives their salary. It's not thousands that I owe, why not go after them?? R493, might seem like nothing to others, but to me it's a lot of money...please can you be a bit more considerate??