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Presuming you have applied for a visa outside of the UK, the relevant information regarding refunds is available here.
What is the visa fee refund policy?
We will only refund your visa fee if you withdraw your application in writing, using the refund request form on visa4UK, before biometrics are submitted and within 3 months and 7 days of the date the application was paid for. Visa fees for applications where submission of biometric information is not required will only be considered for refund where the written notification of withdrawal is received before the physical applications have been either accepted at the visa application centre or received directly at the Visa section. You will not be entitled to a refund if your application is granted for a shorter time period than the period you applied for.
It does not look likely that you will be eligible for a refund for an application for which you already have an appointment.