Your answer has given me big hopes & I will be writing to HMRC.
I am mentioning the year and date they have used for unpaid amount:
Period ending 05-Apr-2005 amount due 2821.60 gbp
Period ending 05-Apr-2005 amount due 780.01 gbp
Period ending 05-Apr-2006 amount due 1795.50 gbp
Period ending 05-Apr-2006 amount due 253.26 GBP
Period ending 05-Apr-2007 amount due 56.38 GBP
Every year we use to phone HMRC with our actual earning at the end of the financial year, but for some reason they kept on paying.
When I became in-eligible for tax credit due to higher income threshold they started chasing me.
I send them few letters back in 2007, then the matter was quiet till June 2014. All of sudden they have send me notice for collection in June 2014 & letter from debt recovery agency on 25-July-2014.
With above details I believe your previous reply still holds.