The sequential postpaid billing doesn't function properly.
It was set to:
in 10 minutes, increment the bill by 10c every minute.
Prior to this, i set a postpaid recharge to $1 for 10 minutes (as i noticed that the sequential billing option is based on the largest amount of time set in the recharge)
However, sequential billing does not work. It rather has the function of time based billing mode, not an incrementation of the costs over time.