How can i get a full refund from a carparts company.?

How can i get a full refund from a carparts company.?
Recently i ordered a part for my car of the internet from a company in GB as it happened i could not get the part in time so i had to cancell it, the problem is they said that i would get a refund but they have not sent it out, now i have just got a bill from the credit card company for £30 and the car parts place will not answer my emails can i do anything about this?.thanks for any help.
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Car Parts|Auto Parts