Non Arrival of Overseas Overpayment cheque.

My mother-in-law, who lives in New Jersey, has had confirmed a significant P800 repayment cheque on behalf of my late father-in-law's estate on 1 July 24. As of today, she has yet to receive it though it was promised to arrive by 23 September. She has tried contacting HMRC but was passed around from department to department for over an hour on an international line and is now of an age where she doesn't cope very well with these things. I have tried speaking with HMRC on her behalf and, despite just asking for advice, was cut off. What can she or me do? Is there a direct line she could call or an e-mail address she use? Thank you.

Hi,
If the payable order has been posted, but not received, we would require confirmation of this in writing. We can then arrange for the payable order to be cancelled. Your mother in law, may, if she wishes, nominate an individual to receive the payment on her behalf (this should be in writing). A letter should be addressed to H.M. Revenue and Customs Pay As You Earn BX9 1AS.
Thank you