I too have an IVA, of which a tax credits overpayment was included of just over £500. My IVA was granted in Feb last year, so 15 months now. On saturday i received a letter from tax credits saying they had no choice but to send enforcements to get payment!!
I rang them yesterday, and they told me that their legal team were having any luck with insolvencies so they were dealing with them seperately!!
It took lots of explaining, rather unimpatiently, to tell them they cannot persue this payment separately as it was in my legally binding IVA, and it was illegal to harrass me for payment now!
They knew about my IVA but hadnt applied for payment, or interest in it. They told me to get back in touch with my IP, so i said no, you do it. I explained that i should have no further contact with my creditors and that it should be through my IP.
He said he'd refer it back to his legal team. What a cheek!
IVA in 2007 - failed in 2008.
BR on 11th Nov 08