Have you downloaded your PDF invoice from Self-serve and reviewed it? That should detail each of the charges leading to the $106 total. You can post a copy here with personal info removed, and the community members will try to explain the charges to you.
@ Nitsa, looks like you changed plans mid-cycle and also went over your included minutes. On page 4 of your pdf it shows how many minutes it is. It's 212 hence the $106. If you look at page 7 of your pdf bill you will see indeed that extra minutes are $0.50.
I think your best best maybe to switch to a plan with unlimited minutes. There 2 options. One for $40 without any data included or $65 a month with 3gb of data included.