in the middle of a "Scenario" I have saved my progress, but how do resume that saved game, I cant find an option to load one, there is only the restart.
In the main screen of the specific route the first option is to continue from your save. Its "Last played".
You'll find though that the service you were currently on will break - the game won't know you are on one (at least I find this with the 1A02/1G11 service)
Yes, there is only one save for the entire game, I have had success in saving a service on GWE by saving whilst loading passengers. The service can then be completed later as normal.