Certified GKH Gardening Expert
Can you include a photo? Depending on what kind of material was used to bag it, this may have led to further infection. A photo will help me to see the damage, and if it can be cured.
For now, this article will help you with the care of these: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm