There are different plans available to suit the amount of traffic your site attracts, but are you on the right plan? How can you check your usage?
Your current months usage can be calculated by adding together "unviewed traffic" and "viewed traffic", for historical months totals select the month from the drop-down box near the top of the page the add the same two figures. Further down that page you can see graphs displaying your historical bandwidth usage - but these graphs do not include the "unviewed traffic", which should be included in your actual total.
Usually high bandwidth usage means your site is getting good traffic - good news. Check the available hosting plans and make sure you are on one that suits your expected usage.
Hint: Exessive bandwidth usage can sometimes be due to hosting large files (photo's, pdf's, audio or particularly video). Keep these file sizes to a minimum while maintaining your required quality. Videos can effectively be hosted by YouTube but displayed within your site, thus saving your bandwidth.