How to obtain CGT Overpayment Refund

I am submitting a Tax Return with a Capital Gain included. The Gain was reported within the 60 days and was overpaid. The overpayment shows on the calculation but it is not actually credited by way of increasing the tax refund due. So how do you reclaim the CGT overpayment?

Hi 

As the systems are not linked you should  telephone 0300 200 3310 to request this.

Thanks