Paying shortfalls in national insurance class 3 problems

Hello, I am having an issue paying my class 3 shortfalls for living abroad between 2005 -2015 via my Barclays bank account, i have been given the sort code and account number, i have already been told that my reference number is my national insurance number then IC and then my surname and initial. My issue is that when i go to make the payment my bank account doesn't let me because it says the reference number isn't what is expected for the account I'm paying into, it seems to be expecting the 20 digit reference code which i haven't been given and never been told about. not sure what to do as everyone i have spoke to via phone call and have read on here says its the reference number that i have said about above. Any help??

Hi,
If you are paying from an overseas bank account then you must pay to the following details: 

•    Business Identifier Code (BIC) - BARCGB22
•    account number (IBAN) - GB49 BARC 2020 4830 9447 93
•    account name - HMRC NIC Receipts

The reference number you must use if you are paying from an overseas bank account is your National Insurance number followed by ‘IC’, your surname then your initial. If your bank limits you to a certain amount of characters, you should use your National Insurance number followed by ‘IC’ and as much of your surname as possible. For Example if your name is Anne Jones, you’d write the reference as QQ123456AICJONESA. If your name is John Douglas-Hamilton and your National Insurance number is QQ123456A, you’d write the reference as QQ123456AICDOUGLAS-HAMILTONJ

However, if you are paying from a UK bank account, you must use the bank details:
•    sort code - 08 32 20
•    account number - 12001004
•    account name - HMRC NIC Receipts

The reference number you will need to use will be an 18 digit Reference number that you can get from us via telephone or webchat.
Please find the contact details below:

Number
0300 200 3500
Overseas
+44 191 203 7010
Open
Monday to Friday: 8am to 6pm
Closed on Saturdays, Sundays and Bank Holidays.

Webchat-Ask HMRC online - Ask HMRC 
Thank you.