Confirmation of receipt of letter and further information sent to HMRC regarding NICs

Hi there, I submitted an online form CF83 that has been been recorded as received in my personal tax account online. I have since posted a registered letter, dated 07/05/24, to HMRC detailing some further information to be attached to the CF83. Can you tell me if the registered letter has been received by HMRC? As It hasn't been recorded as received on my tax account. I've received a letter regarding NICs for years 2015 - 2024. And I've been told that a subsequent letter was also sent to me on the 13/05/2024 regarding payments amounts for the years c. 2010 - 2024. I haven't received this latest letter so HMRC are sending me another copy in case it has been lost in the post. Can you tell me if this latest letter from HMRC is a response to the CF83 and also the additional information I sent by registered post? I don't want to start making payments before all the information I have submitted has been taken into consideration. Many thanks for your help

Hi,
In order for us to answer we require further details, you therefore need to contact the Customer Helpline.
Please find the contact details in the link below:
National Insurance Enquiries helpline
Thank you.