Diamonds falling off

My husband purchased a sterling silver ring set (3 bands and diamonds) in January 2015. Shortly after, 1 diamond fell off. I visited several stores and they advised that they cannot assist. A second diamond fell off in 2017 and now a 3rd diamond has fell off. No stores are able to assist. I am appalled by the nonchalant attitude and service of the staff. They are adamant that nothing can be done to assist me - nor am I able to obtain a refund. I will never purchase from American Swiss again.