The panning(swiping) gesture cannot be turned off, this is the intended behavior of the calendar when range selection mode is active.
However I completely agree with you that pinching out is not especially intuitive action for navigation between months, so may I propose a bit different approach.
Consider implementing navigation buttons above the calendar which provide easy and intuitive navigation.
This way you can keep the swipe gesture and still have a straightforward navigation.
The attached screenshot is an example of this exact scenario with the only difference that there are navigation buttons for both years and months.
Should you have any further questions, write back any time.
Telerik by Progress