Gordon Bennett

I made a claim to the overpayment relief department back in January for tax paid on a PPI pay-out. The claim was made in writing, with the relevant documentation included. Declaration made, signed and dated. It's been 7 months and I've heard nothing back. How do I contact the department ? I know they've received it as it was sent via recorded signed for mail. I've tried writing, emailing, phoning but nothing. The only reply I've had is via X (twitter) and all they say is that I should have heard back by now and give me links that I've already exhausted Any help would be greatly appreciated