Hi Gordon,
If it’s just the case that you’ve accidentally used the wrong VAT type, you can credit note the invoice and raise again with the right figures so you can allocate the payment received. You’ll need to switch to ‘Classic’ invoicing to raise a credit note for the moment.
If you believe the VAT was added correctly when the invoice was issued, we’ll need the invoice number so we can look into this for you (you can email us at feedback@crunch.co.uk and we’ll take a look).
Hope this is helpful!