Pregant with the coil and been told its not viable

Hi guys had a coil put in on the 5th of july and found out i was pregnant on the 13th of july the only time ive had sex was the 3rd of july condom must have split or been.a dud i dont know but as procedure my doctor sent me for an.early scan to check it wasnt ectopic on the 28th of july and she bluntly told me its non viable theres no heart beat and juding by the size it was almost 7 weeks i mean the dates just dont add up theres no.way i could be 7 weeks. could i just not be far enough along for a heart beat to show up on the 28th and i have no last period to go by as im 3 months post partum so that not very helpful i personallythink i could only be 5 weeks