Over Payment Relief claim.

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

Hi Gordon,
Please contact our helpline on 0300 200 3310 or contact our webchat facility at Contact HMRC., to progress chase your repayment claim.
Thank you.