Sherwin-Williams

I recently bought a bucket of Super paint, paint and primer and after applying to an existing wall, previously cleaned, it completely failed! The last application was 4 days ago, and If I clean the wall with a wet rag it comes off! I applied 3 coats (let the paint dry in between 12 hours). One of your representatives passed by and said that it was my fault, since I had not sanded the wall previously. The wall was previously painted with a flat finish and was cleaned before the application. I had never had this issue before with any other latex paint and was shocked that the representative insisted that if if did not sanded the entire wall the latex paint will continue to fail. At this point I will not use Sherwin Williams again. I will buy another paint from another brand and will test it. I am sure it will not fail... This paint sucks...