So many image resizes & thumbnails getting cropped ??

Whenever I upload any image on my website, it gets re-sized to many dimensions. This is resulting in sometimes 7-9 files if the original image is big enough.
This do not happen when I switch to twenty fifteen theme, but when I switch back to customizr, the issue is back again. I actually do not want these much resizes to my images.
I just want to disable this feature for future uploads and delete all the previous resizes of the images. How can I achieve this.??

I am also having issue on post thumbnails getting cropped. (i have unchecked the option of cropping thumbnails in settings->media.

Please help.