just coz they sold you 120mb dont mean your getting the full 120mb 24 hours of the day there peak times and the speed will slow and thats will all companies ..in my area i had virgin 120mb and at peak time was a joke ..but bt 80mb was faster and never lost speed at peak times like virgin
even when i did get peaked, i was still getting 97mb/s

and when i wasn't i was getting over 120 LOL