Seems like an adjustment to equate the total that you have paid to the total of the invoices you have received. Looks like some sort of gst evasion as they claim plan charges+gst but provide invoices that mention some other things like platform charges.
As said before 841.36 + 160.46 is the total that you have paid for the silver plan. Same as 849*1.18. But due to their jugglery they are only paying 128.35 as gst vs 152.82 which they should be paying for 18% of 849. Simple GST evasion.