Hi marie48
Welcome to the Community Forums.
Sorry to hear of your billing concerns.
Does your Virgin Media bill breakdown show the amount owed is the same amount you paid? If you pay manually and make payment under the amount that was due from a bill, the difference in the amount not paid will be added to the next bill and continue to do so until the full payment has been made for any outstanding bill amount for previous months.
Please let us know if this answers your query and if not we can assist further if you need.