Default

I was living at an address and I moved out of the property in december, 2017, I had nowhere to go at that point in time so couldn't provide an address to the housing agency as to where I was going and just wrote "N/A", fast foward 6 months and I check my credit report and find out there is a default on my account from British Gas for £700. Up until the point I moved out, my bills were paid in full, and I had 0 debt on the account, I imagined I had paid everything that I had needed too. I had no notification of debt, or notice of default, granted that I didn't give them an address. I also find it really hard to believe that I could be paying my gas bill whilst I was living there for 6 months and still end up with £700 left to pay. I was a single guy living alone and only had the heating on for 3 of the months I was living there(3months was summer time) regardless is there anything I can do about this default on my account? I want to get a morgage for a house within the next couple years and this default is the only thing on my account. Could I still get a morgage with a settled default?