Default advice

Hi there, I'm after some advice. Due to the breakdown of my marriage in 2014 I sought financial advice from Step Change who helped me to set up a DMP to manage the outstanding debts that I had at that time. I had 3 outstanding debts with LLoyds bank - a credit card, a personal loan and an overdraft which were added to the plan. I opened a new account with the Co-Op for my salary and bills to be paid in and out of and I was in touch with LLoyds throughout this time explaining what had happened and why. In October 2015 I had to make a formal complaint to LLoyds as the interest and charges they were adding to my loan account each month exceeded the amount that I was able to repay and so the debt was not reducing. They advised me that a formal complaint was the only way to resolve this. They eventually issued a default on the account and agreed to freeze the interest and charges. Throughout this time, Step Change continued to make payments at the agreed level on all of the accounts. In August 2017 Lloyds issued a default notice on my current account - no payments had been missed but they explained that they were going to move it to their recoveries department and had to issue this default in order to do this. I assumed that I had no alternative but to accept this. Now, I am in the process of trying to remortgage which should mean that I will be able to clear all of my outstanding debts but the default from Aug 2017 is blocking my application. I have tried to discuss the matter with LLoyds but they say they have acted legally and I have no grounds to dispute the default. My argument is that the default should have been issued in 2014/15 not 2017, that they may have acted legally but not fairly as they have made it appear that I defaulted on my agreement with them in Aug 2017. Sorry for the length of this post but any advice would be hugely appreciated!