No response received relating to overseas NI contributions submitted in Jan, what to do?

I completed the necessary online submission to see if I would be able to submit a lower class of NI contributions as was working overseas in January and received confirmation through a 12 digit reference number. The site informs me that I should have received a response by March 1st but I have yet to. I am set up for email communication but nothing received there or my US postal address as they state will write to me. This morning I tried calling the 0191 number several times, getting the automated agent, only to be informed that unable to help and drop the call. Appreciate that it's a busy time but ultimately I am trying to get clarification on how much I need to pay to top up so I can make payment but all roads seem blocked. Any advice/insight would be appreciated.

Hi,
If a CF83 has been actioned and a response issued, you will need to contact National Insurance to discuss options further you can use the webchat function through gov.uk to contact an adviser. We only issue this information via post. Please ensure your address we issue your mail to is fully up to date. 
You can also call, if from the UK you can call 0300 200 3500 or +44 191 203 7010 if calling from abroad. You can also write in to:
PT Operations North East England 
HM Revenue and Customs
BX9 1AN
Letters need to include you full name, National insurance number, Date of Birth, full current address and be dated and signed. Please inform them of your issue and a caseworker will provide further assistance. 
Thank you.
 

I have received a reply to my application and I have made a request for a call back Pensions. Are 31 days added to the date from when they phone you to be able to pay the voluntary contributions?