debt

We made agreement last year in August 2019 that i will pay them on monthly basis an amount of R400 for 3 months as they gave me discount. They should deduct the amount starting from 13 September 2019, they did deduct on September. The following month which is October they were supposed to deduct on 15 October as per our agreement. They went to deduct on the 11th October 2019 which we never agreed about and they didnt find any funds.They cancelled the discount while it is not my mistake but theirs. They have been telling me they will solve the problem but they are now theatening me with summons.pls help.