Disgusting customer service and exchange policy!

Extremly bad customer service at Babycity Greenpoint! I called the branch on the 22 August and asked if they have the Snuggletime Bamboopaedic mattress 140x70cm. I have been told that they still have 3x of these mattresses in stock at Sable Square. I went to Sable Square and asked for the same mattress with the same measurements and was given a mattress which is 1040mmx700m. Unfortunately I only noticed at home that I have been given the incorrect size. I then went to exchange it and have been told that Baby City does not at all sell the mattress I need and that I cannot return the one I bought because the seal has been opened, which I should have been advised of when I bought it. I have basically been given the incorrect information by staff twice, I have been sold the incorrect product and then I have been denied a refund! If you cannot resell the mattress because it has been opened, you should make sure that you sell the correct product in the first place! Also the Manager at Green Point branch was extremely rude and has no customer skills whatsoever!!