Unsure if to contact creditor over default and debt

Hey guys,

First time posting. Would like to wish you all a happy new year first of all.

So where do I start?
6 years ago my partner and I entered into an IVA on the 23rd Sept 2011. Mortgage followed by Recession and new born forced us into this situation. This failed later on and we made contact with our known creditors at the time and have paid them all back over the past years whilst attempting to rebuild our credit report.
The IVA status has now been removed from the register and credit reports so we can finally make an attempt to live like the norm.
We now wish to sell and buy a bigger property... Additional child has come along.
Speaking to mortgage advisor they require a copy of our credit reports.
Here's where my issue lies... So, signing up and checking these reports I have found a closed account with a default on it with the balance of just over 4k (barclays partner finance/clydesdale partner finance) the start date of the account is 8th Nov 2008.
We were under the impression this was under the IVA and an account will go into default once in an IVA if not before, and this would have been removed.
Apparently on the credit files this went into default March 2013 meaning the default won't come off until March 2019.
As we failed the IVA and sorted out finances ourselves (we waited for creditors to get in touch with us then worked with them) we were under the impression we were getting somewhere, all creditors taken care of and happy and all paperwork for which was settled and no longer any use (school boy error I know now)
Please bare in mind Barclays nor clydesdale have never made any attempt to contact me not chase me for this balance whatsoever even to this day and I'm 100% certain they have changed the default date, possibly so I would get in touch with them... Not sure. But I have no paperwork no prove this. I was completely oblivious of the debt until recently.
I don't want to voluntarily get in touch with them if I can avoid it but I'm unsure what affect this will have on my partner and I attempted to apply for another mortgage.

Please can someone help with any advice on this. I'm completely stumped.

Thanks in advance but as you can see it's a bit of a strange one.