Groupon SA
Says they refunded but it's not in my account

I purchased 2 x Unnique Keratin Hair Straighening Kits late last year with the intention of doing the DIY treatment at home over the holidays. When unpacking the products discovered that Formaldehyde is one of the main ingredients without stating the concentration, legal limit is under 10%. Packaging also says clearly on the bottle 'for professional use only and to be used by a licensed technician. This is clearly NOT a DIY product and is one only to be used by licensed professionals. They agreed to collect the goods and refund me in full. They're saying they refunded on the 21st January but there's nothing reflecting in my account. They are very slow when replying to emails and often I've had to email again in a threatening way to get a response from them. I have thoroughly checked my account around the 21st of Jan, there's definately no refund. I want my money back so I can put this bad experience behind me.