Finally, i got my money back and orange did not charge me for the phone ! Thank you all for your suggestions, really appreciate you providing your help and views!

Yes, i do have the box in which the first phone came and the IMIE number is different from the one they sent back. I could say the same that they switched phones and sent to me a different one. But i am afraid they do not believe me.

I had an upgrade with Orange for Samsung S5 phone and I was sent a new phone. After 2-3 weeks the phone stopped working and i called up orange in return they send me a replacement handset. I was told that a replacement handset shall be sent by a courier and I should hand over the faulty phone to the same courier person. I received the new handset and handed over the old handset as i was told. After 1 Month i receive a different faulty handset and been told that i returned a different phone to orange then the one they gave me. I did not switch the handset at all still being accused of doing so and unfortunately i dont have any way to prove it. The phone i received now has screen broken, the faulty handset i returned had charging issues and the phone was in very good condition. When i contacted orange they are saying i didnt not return them original handset and hence they charged me 300 gbp on my monthly bill. I called up Orange 8-10 times to explain them myside of the story but no one would believe and when i tried to end the contract i am told i should be paying the remainder of the contract fee which is 450 GBP in addition to giving away the handsets I have been with ORANGE for last 5-6 years and have used best phones but this incident has inclined me to end this relationship with them and move onto other service providers. Others be warned when you return any handset back to ORANGE take a snap of the phone you returning which IMIE displayed and also take a snap while you handing it over to the person. My advice is never ever do business with ORANGE. I am very upset and disturbed by this incident.