Notifying a change in income

Should be a change of circumstances id think,but you could ring to check first so they dont mess you about.I cant plead enough how important it is TO MAKE SURE YOU PHOTOCOPY ALL OR ANY FORMS  OR LETTERS YOU SEND THEM- also MAKE A NOTE OF THE NAME OF ANYONE YOU SPEAK TO- I say this to warn you as i sent in 3 different forms at different times( plus made calls) when my youngest son moved from higher rate DLA to middle rate AND I DID TELL THEM THIS AT THE TIME-in fact i even got DLA dept to ring income support& carers allowance- but the DWP idiots got it wrong and then ended up few mths down the line by saying i had never told them and claimed back £2,600  from me that they say was overpaid but  it WASNT my fault! Because id not photocopied all my forms/letters to them or wrote down to whom id spoken-and on what days/times/which depts etc i had no proof it was THEM who had made the mistake! I implore you -dont make the same mistake i did- make sure you copy and log everything.I will in future!