I don't remember clearly about what happened earlier? Wouldn't they steal more if it did happen?

Okay so in my house our Sky + is missing, the card. My sister, her boyfriend, my dad and I have been the only ones in the house and we're unsure on how it could have happened and my mother has been pestering me "did you leave the door open? Are you sure you didn't?" And I kept saying no, I have not left the doors open (I was in the house first after my mother left for work, my sister stayed at her boyfriend's) And I got quite frustrated but now I'm worried, I remember opening the door and offering my cat to go outside but he refused, I don't quite recall closing the door properly, I think I walked past it with it open but not fully, like pushed up against the hinges but not closed properly and I don't remember if this was today or another day, my mind is muddled and now I'm worried that it was today that happened and someone came in the house when I was in my room listening to music but, wouldn't the people steal more than just a Sky + card? Or just leave as soon as they heard my music playing knowing someone was inside? I mean I remember making a sausage sandwich and watching TV for a while then turning the entire thing off, Sky and TV and walking past the door but if I remember right I think I thought "I won't close the door Steph is coming home" or something like that but I honestly can't remember but I think that happened, what should I do? My brother and his girlfriend had a funny encounter too, someone left two flowers on their table when they were out and they don't know who? Any sort of help would be muchly appreciated.