I feel you pain, but you don't get ticketed immediately when you use Viking Air. You are ticketed when somewhere under 60-75 days from the actual flights.
I would not immediately blame Viking or Viking Air. Obviously your original routing changed or cancelled and the re-routing happened. If you were originally flying BA then something happened to your return flights with BA that caused the change.
I don't believe that someone is sitting at Viking Air wanting to mess with you so they change the flights - this would be initiated by the airline and Viking move to reroute you so you have flights.
We often book way out, but in that booking way out, there can be many flight changes before the actual flight. Sometimes, yes, it is frustrating because we carefully chose our routes and in some cases even the aircraft type that we were flying and we end up with a totally different itinerary from what we originally booked.
First things first - if you used a TA go through them, but be on the phone with the TA when they call Viking Air Plus. Find out what happened. Before that search the flights YOU want again yourself. When you are on with Viking Air Plus and the TA, outline the flights you want and have them change them. Before the flights are ticketed, you can many any changes you want.