failed to honour promise

We purchased a Granite Tombstone for our brother for Tombco Vryburg in 2012/2013 on instalments. We paid off the Stone in 2013 and installed in 2013. just two months later the stone was peeling, we realised its because the stone was painted, so the paint is coming off. We went and complained with the supplier,she gave us a form to fill after a year of complaining and she still promised to fix the stone. to this day nothing has really happened and she still keep promising. I have called, went in to the store, and nothing has really helped.