Return from May 2015 still not refunded

I've order goods from Groupon on 11 May and paid by credit card. The order was cancelled straight away with the online self help steps. I've called them 3 times to ensure the order was cancelled. They told me its ok, they will cancel the order and refund me. Some days later, they delivered the parcel and didn't want to except the fact that i've cancelled my order and do not want to accept the goods. i've requested them to collect the order again as I cancel the order. I've waited for ever for them to come and collect it. to date they have not refunded me yet.