MIB failure to refund after online sales error

MIB, had a sale on, i purchase the products and paid. <br> <br> unfortunately their system had an error and the discount want too much. they enquired if i wanted to pay the difference of get the refund. <br> <br> i had opted for the refund. they have refunded one of the two orders since 8 May 2015. <br> i have sent various emails, with responses stating that they will deal with it, when i call the service centre no the subscriber you have dialed is not available....<br> <br> i am tired of requesting my money for their errors, either refund me or ship the product!!!