Juno Records wont refund - what are my rights?

Hi

Can anyone help me with my consumer rights?

I purchased an import USA item from the Juno Records (https://www.juno.co.uk), however when the item arrived they sent me a standard UK issue - it is the wrong item.
I requested that I return the item and they resend me the correct item, or I get a refund:

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Hi,
Apologies for the problems with this.

Normally we would just send a replacement, but unfortuantely these are all
mislabelled and we do not have the correct US issued copy.

Please mail us if you want to return this for a full credit/refund and we
will set this up for you and email you an Authorised Returns number.

Thanks,

Sales Dept.

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Hi,

United Kingdom

We will give you a store credit for the cost of the record and the return
postage. This will automatically be deducted from your next order after we
receive the return.

Thanks,

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Ok that all seems fine but then when I mailed them again for the returns they say they will only issue me a store credit - I do not want anything else from them and its not my fault they sent me the wrong item and cannot supply the correct item!

Any ideas on what I can do?

Thanks