Walmart complaint: Air mattress

Bought air mattress from walmart brand name Ozark Trail. It starts to deflate by itself as soon as you are done pumping the air in. It deflate in middle of the night while you are sleeping on it. I spent $80 for this mattress. Walmart employee refused to return or exchange by clearly saying contact manufacturer because they can only exchange with in 30 days after purchase. However, receipt clearly says with in 90 days after purchase i can do return or exchange, there is no 30 days policy on the receipt. Please help me here i feel like they made me fool. Contacted walmart head office, they said try to exchange in different walmart not the one you made purchase with. How manufacturer is going to exchange? if walmart is not taking responsibility for their products they are selling. More over walmart have to clearly print their return or exchange policy on back of the receipt, it is 90 days or 30 days.