When a text message is sent , it doesn't always deliver it straight away for various reasons ie busy network causing delays or maybe the person's phone is switched off. When a sim card has been reported lost or stolen and a replacement is requested , it immediately cancels out the previous sim so any messages sent to that number will be returned as a failed message. However , as text messages can float about for up to 72 hours from when sent before either being delivered or returned as message failed , it will show as having been sent from your phone. Did your friend send it less than 72 hours ago ? If so , it may still return it as failed. If not , then i'm a bit baffled. She did send it to the right number eh , lol ?
Have you blocked the handset with your network as well ? If not , then you should ask them to do that because it renders the phone useless so that whoever the toerag is who's got it won't even be able to use it if they have taken out the sim and put another in. It will be blocked. At the risk of asking a stupid question as well , have you reported it to the police ? My sister had her phone stolen at school but saw the little creep who had it and recognised it as hers. She could prove it was hers because of the IMEI number and IMSI number which I had told her to always keep a note of. Even though he had changed cards , she could prove beyond all reasonable doubt that it was hers. I do hope the guy you're hoping to hear from gets in touch. Chin up and good luck x