IS and Carers Allowance

I was just wondering if I am thinking along the right lines with this case

Client’s son gets DLA and she was getting IS/CA - c.45/55pw split.

Client unfortunately was late in submitting a DLA renewal and her claim stopped. A new award was then made which was backdated to the date her previous claim had stopped.

Unfortunately in the meantime her CA was stopped. She didn’t realise and continued to receive the 45pw IS as she did not inform the DWP that her CA had stopped.

In Jan 2013 DWP appeared to realise what was happening and stopped her IS claim. We made new claim for IS and reclaimed CA. Client is now back in receipt of both.

However client has now been told that she has been overpaid 2572 of IS from period of 23/11/11 to 29/01/13. I haven’t managed to get exact confirmation from DWP and client states that she didn’t get a decision letter but this corresponds to a decision that she wasn’t entitled to any of the IS that she received when she was not getting CA.

Client’s applicable amount for her IS was made up of c.70 personal allowance and c.30 Carer Premium. I am confident that when her CA stopped she continued to be entitled to the basic amount of IS as she was providing substantial care but she lost entitlement to her Carer Premium.

What I’m not sure about is how much she has been overpaid/underpaid. I am pretty certain that of the 45pw overpayment, 15pw has not been overpaid, as this is the remaining IS added to CA to get her to her personal allowance. However she was not actually getting CA! So really for this whole period she was actually being underpaid £25pw IS!

I am wondering what her chances are of:
a) getting the overpayment written off by the DWP calculating her underlying entitlement to IS
b) getting payment of the £25pw she was underpaid after her CA stopped.

My feeling is that both of the above rely on the argument that the non-communication of the stopping of her CA to the IS department constituted an official error. My understanding is that previously arguments such as these have not been successful but I was just wondering if there was any additional communication lines between Income Support and the Carers Allowance Unit that might support such an argument.

Any thoughts welcomed