negative score

I'm fuming i had an account which was in my name and email  it was a sim for my husband a  few months ago my husband left on negative terms I stopped paying for his sim tried to contact you numerous times you then sent my payments off to a debt collection company for £14.00 which was pathetic in my views i then spoke to a lady from Id mobile who sorted it all out even refunded me my 14.00 but then as I had a missed payment on my credit file she assured me that this would be amended well I'm still waiting as my missed payment that I didn't miss is still showing on my credit file negative i waited 6 years to get a credit file as I myself had an Iva and I've got a lovely credit file apart from you so I would appreciate you doing what the lady told me she was doing and take that missed payment off my file ASAP thabks