How to continue playing career? (Pls, help)

[Dinoboy AG]

Someone, please, help me. I don't know what to do. I choosed 1939 year, 7th flotila, number of ship is U-53. I finished one crusade. I did main mission. I destroyed 3 enemy's trading ships and did both "enter the AL36 zone" and "patrol this zone for 24 hours" missions, they were green, and by the end of the crusade, when I checked my missions, and saw, that both is completed I had about 10% of fuel and I was far from the place where I was started. So, I clicked to end the mission. In the menu I saw, that it was completed and it's statistics. Then, I wanted to continue playing, but when I click "missions", I see the same objectives that I completed. I can't change the flotila, and idk how to keep moving and start next new mission. What am I supposed to do? Pls, help.