I will be looking at a right to buy mortgage. Value £80k, Mortgage i have to find £50K Would that make a difference and can anyone suggest the best line of looking for a mortgage. Would a broker be better than a main line of credit?

Looking for a bit of advice here. Am going for a mortgage in October and am i the process of trying to clean my credit file. There are a couple of defaults that i have no idea i had so i have challenged them without saying i owe the debt using a CCA letter. Now 2 others were disputed back in 2009 by myself. One with Virgin media the other with Monument. I have now again sent CCA Letters to them but i am now kinda thinking that i have also accepted the debt as i have refered back to 2009 in the letter. Have i shot myself in the foot with this? Would it be better to let leave alone or fight? Also i have 2 defaults registered with 2 different comapnies t mobile and lowell for 1 debt can this be correct? Any advice on the best way to clean things up will be appriciated.