Back dated spd

Hi all .I recived a phone call today  advising I am.entitled  to severe disability  premium  and have be advised they have worked out I'm owed back dated money around 7 grand   but they said it's from 6 November last year so around 58 weeks of back dating  so if the sdp payment is 64 pound that would work out at around 3700 not 7000 I only ask as it's over the 5000 they have to send it higher to have it worked out and realised  meaning it will take  a lot longer  .anyone on here can work out why why would be 7 Grand is there other premiums that go with it