sorry, i had used paragraphs but it doesnt seem to have posted correctly

Hi AllThis is my first time posting so spologies if this is in the wrong place.I have just been checking my credit file on credit expert and an entry has been added by MKDP LLP on 26th February saying that I have an account in default. I have never heard of these people and have not received any correspondance from them, i moved address last october but my mail has been being forwarded so if they had written to me i would have received it. What do i do now? I have emailed credit expert to see if they can provide any more information but other than that i dont know where to start. Thanks