They probably already know about the £2,220 and it will have gone towards part of your pension entitlement.
As the state pension is currently £102 p/w and yours will only be £83, there is possibly scope to make top up payments to improve your pension.
i think the reference to additional earnings relates to your entitlement to the state second pension (used to be called SERPS- maybe you were 'contracted out' of that.
I'm not sure why you don't get the full state pension- presumably you don't have sufficient years' NI contributions.
Did you pay the reduced married womens stamp? Do you have children that are now grown up because you may be able to claim for the years you didnt work to stay at home with them. The additional pension is the contracted in bit so I think you may have contracted out and if you did then you should also receive a pension from elsewhere. If this is the only pension you have and only small savings then you should be able to claim pension credit.
I never understood the damn thing when it came up all those years ago but then yu never think about these things when you're 30 do you factor.
I checked this afternoon and I do actually get £107 a week, so I think it's ok.