price charged not what was quoted for home internet!

All carriers have a bill and use cycle. You'll have a prorated charge for a partial use cycle. Your first bill in general will always be higher unless you started the plan exactly on the first day of the use cycle. 

For example you started your plan on the 5th, but T-Mobile has the use cycle on the 14th. 

You will be billed the 5-14 + 1 month. From there you use cycle ends on the 14th and no prorate unless you add features in the mid of your use cycle(they generally start it on your next cycle unless you express you want it at that moment for this reason).