It seems all Internet access is satellite based, so quite expensive:
Saint Helena Island Info: All about St Helena, in the South Atlantic Ocean ? Communications
“State of the Island” report, 2015
St Helena’s isolation and reliance on satellite technology, means that internet services are limited and expensive compared to many countries, and are a major barrier to development. The top residential package offered in St Helena provides 13.3 megabytes of data at a speed of 1.5 megabits per second, and costs £180.50 per month.
So your 40 mb (megabits? megabytes?) is several months worth of data at £180.50 per month.