How do you remove a black mark on your credit reference ??

Some time ago my wife k out a loan , which due to finacial difficulties she has now defaulted on , this has been sorted through a consolidation process and is now paying these debts off . recently i have found that because i sd guarantor on a loan i have also been blacklisted by her bank , and now unable to recieve credit in my own right ,although the debt consolidation company reassured us that i would not be affected , how do i clear my name from this blacklist !!
Answer
With a rubber.