As Transam writes, best to call them. When you give them your NI number they will know all about you. I used the AIS number 00500 and was quite cheap, about 25 mins call time . After 10am UK time seems best and maybe not on Mondays.... I was just in a call queue for a few mins too.
I spoke to them about my pension payments here. Now going to Bangkok Bank wef: 1 Sep.