Thank you very much for your answer.
Unfortunately I do not offer a telephone service. The money will be returned to you within the next few days.
Your consideration with the mechanism that changes the gears is already correct, either it jams, is adjusted, or the clutch no longer separates cleanly.
Often it is only a matter of training the so-called actuator (this is the device that takes over the clutch and shifting). A workshop can teach the actuator again. It then learns again where the individual gears are and where the grinding point of the clutch is.
If this does not help, the clutch must be checked by the workshop and replaced if necessary. If the clutch is ok, the actuator and the gearbox must be examined more closely, whereby it must be said that the actuators are very often the cause. This would then have to be replaced.
I would be very happy about a rating with 5 stars over the star bar at the top of the page, without this rating the site operator does not pay us experts.