You have an issue with trimming B-spline surfaces using Trim surface tool. The surface remains unchanged.
There might be several reasons for this failure, but very common one is that elements are out of Solid Working Area (SWA) of model (1 km), and far away from origin of the model. Surface modification tools work well only when you work within defined SWA. Surfaces need to be moved close to Origin to get them close to SWA range.
Here you will find more information about Solid Working Area (SWA):