I am disappointed - up to this place I enjoyed myself, now I will claim my money back.
You've got to be kidding me. Because you've encountered a section in the game that to you is slightly more challenging, you immediately want your money back (even considering you've already got to enjoy about half of the game)? If everyone shared your attitude, no game developer would ever make a profit.
Have you ever been on a swing? If so, you can solve this puzzle: you just have to time your movements.
Of the gameplay in Machinarium, this particular game mechanic made me smile. It's a clever use of the character's abilities and the solution can be deduced. This was a part of the game that made Machinarium -- besides its visuals and music -- so special to me.
I'm sorry, but I'm just unable to comprehend how you want a complete refund because of it.