Rach ,
Hope I have this correct,
1. In Feb you agreed 1985.
2. In June&July you paid 1827.
3, In Sept Start took out 1827.
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Start are entitled to wonder what is going on .
Can you update the small shortfall.?
If you can write (keep copy) and offer to send the small difference and keep up the 1985.
If they require new SFS , its not really a big deal unless your circumstances have changed.
If you havn,t kept a copy of old SFS ask them for a copy and recopy to new SFS .
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I know its a nuisance but in fairness , you changed the rules .