The charges are not for the cartridges, they are based on the pages printed and your plan (either 50, 100 or 300 pages per month). The automatic ink shipments are generally triggered if the system detects that you have less than two months of ink remaining at current recent usage rates. If you had a lot of printing (especially with photo's, which use more ink) it may have triggered an additional shipment. The shipments of cartridges should automatically adjust themselves over time.