Voluntary NIC payments gone missing

Hello, I have a client who is self employed. His NIC contributions were low for a number of years. For the 2016-18 tax years he has paid across the Class 2 NIC due and outstanding but this payment is not showing on his NIC account within his Personal tax account. The payment was paid on 28 March 2022. Please advise how to check these contributions have been accurately applied. Best Debby

Hello, I have tried to ring the NIC helpline twice today. The first time the line cut me off saying the line was too busy - 16:30. I tried calling again and was able to hold on until being cut off for being too busy again at 17:45. Can someone deal with my query please?