What is the best way to appeal

Hi All,

I hope someone can help, i need to know the best way to appeal to Santander, i have a mortgage with them in my name and my ex's name, she no longer lives there and she doesnt have an income. me and my wife (who does have an income) want to take my ex off the mortgage and put my wife on the mortgage, so in the real world it reduces Santanders risk as my wife works and has an income, where my ex does not have an income... however because i have a default on a credit card, santander said they will not take my ex off the mortgage and put my wife on the mortgage, leaving me no choice but to sell the house. i have been told i can appeal to the underwriters, but only once, so do i get a lawyer or someone to appeal for me or whats the best way to handle it.
thanks for your help..