Rejected from Credit?

I bought a house in August and I have just put my name down on 0% interest free finance on a sofa but got rejected. They wouldnt explain why but friends and family have suggested that it could be one of many things, havent paid enough months on my mortgage, not on the electoral register yet and have no landline. I have always paid my credit card bills on time so I think it is something to do with buying this house. How can I make sure that I can be accepted for credit in future as I will have a black mark against my name for the next few months. I have now sent off my information to be on the electoral register and am setting up a landline this weekend. What else could I do?