im having the same issue with EE, can i ask how you got them to remove the marker?

Hi looking for some help. I have worked for an agency for 5 years and have been offered a contract with the company I have been on assignment with. As part of the pre employment checks they have informed they cannot continue with the offer of employment as I have a cifas marker. 7 days of worry no idea what this was to find that EE have slapped a cat 6 fraud marker under evasion of payment. I did in 2015 take out a contract phone with them on the understanding that it was pay nothing up front then 18 quid a month. Sounds good but on day it arrived they demanded 150 pound up front before I can use it. Nowhere on anything I received stated this. Poor judgment on my part but I took the huff and never payed the amount t required. I also never returned the handset. I never heard from them again and forgot all about it until now. Anyone please advise me how I can remove this. I really don't understand how this is fraud. Is it fraud? I've checked my application and all details provided were correct. I'm totally at a loss and over the head of a 150 pounds I'm now potentially loosing out on 26 grand a year job because of this. Any help advice appreciated. Thanks Mark