Mattress sag

I purchased the Jenson bed frame from you in March, I bought a mattress from elsewhere new at the same time. Due to the Jenson beds slats this is causing my mattress to sag in the middle. I believed it to originally be the mattress but I have taken the mattress off and found its not the mattress with a sag, it's caused by the slats on the bed frame. I am unhappy with this product especially as last week a foot broke, considering this product is 2 months old I feel this is extremely unsatisfactory. I would like to have the product removed and a refund for the product, as this is causing me great back pain and discomfort.