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What is your query please?
Who made the error with the guarantor's email address?
Thank you. Did they give the flat to someone else?
If they refuse to utilise the holding fee for another property, you may then consider sending them a legal demand as it is not your fault that they did not correct the email address.
At the moment, it seems that you are still trying to negotiate with them and I hope it goes well, otherwise you may send them a letter demanding the money back and giving them say 21 days to return the money (14 days is the minimum required by law).
If they still fail to refund, you may file a claim online at www.moneyclaim.gov.uk
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