So there are a couple of things here :
1. The container of the image is square, so if you make your images square they won't be cut by the container.
2. If you want to keep the same dimensions of the images you should correct the container's dimensions. As I see on your website, the images are the same proportions (currently 229x345). You should go to the administration, find Plugins/Nop Allure Theme/Settings and add these lines of code in the "Custom Head Styles" textarea :
.item-box .product-item .picture a:before,
.product-grid .item-box .hover-details:before {
padding-top: 150.7%;
}
now the proportions of the container matches the proportions of your images.
3. Hint: after doing the stuff from the second point, change the width of your "Category thumbnail image size" to 345 from the administration in "Configuration/Settings/Media settings", so that the images fully stretch inside the container in mobile.
Best regards
