I am a barrister. I used to work for the Financial Ombudsman Service. I can help with this.
Did you make the purchase using a credit or debit card?
That's good. This means you can make a claim against your credit card provider just as if it was the supplier i.e. the ticket company. Your credit card company might try and say you need to first go through a claim procedure with the supplier - this is not true.
In relation to the substantive claim, without seeing the documents, I cannot advise whether there has been a breach of contract or not. I would say, initially, the over charge, is in itself not grounds which I would consider hugely valid.
However, what I recommend you do is contact your credit card company, if they do not refund. Refer the case to the Financial Ombudsman Service. It is free and your case comes within their jurisdiction. If they assess your claim as valid, they will order the credit card company to make a refund.
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Can you press the accept button please, thank you