How to activate my Iphone 3gs?

I brought my iphone from Tescos and stayed with a tesco sim card for about 2 years and about 6 months ago i decided to transfer to Orange.

When i transfered to orange i was supposed to unlock my phone. Now i had two options of how to unlock it: 1 - called in Tescos and they said they'll unlock it (send a letter to me of how to unlock it) within 5- 30 days or something similar. My option 2 was to take it to a shop down the street, pay them and have it unlocked in an hour.

I took the second option, and unfortunately received that letter of how to unlock my phone within 2 days and regretted having unlocked it through the shops (because i paid £20)

They also down-dated the phone which made me get NO Notifications of apps like Whatsapp or Kik and that really bothered me.
So yesterday i decided to update it with my laptop (which will remove the unlock) and then i'll phone tescos again to have it unlocked by them even if it would take long.

What happened though was that once i emptied everything from the phone i was unable to activate it. The reason why is it says it's supposed to have a valid sim card on it, though it isn't working in any of my sim cards (Tesco sim AND Orange sim).
So what am i supposed to do?

I brought this phone 3 years ago so the warranty from tesco is over so if i'd need to go to a shop and have them fix it for me should i go to Tesco or the Apple store? (it says "Contact the Apple store if this message keeps showing up")

Go to Apple store, they will help to fix the problem.

I'm sorry to say the Apple Store will not be able to help when it comes to unlocking the phone.

What has happened the phone has been unofficially unlocked (known as Jailbreaking) by a third party business and Apple don't support that option meaning connect it to iTunes and you lose the unlocked phone. If you were given this advice via Tesco by an adviser this was false information which led you to do what you did, but will be your word against his/hers, but worth a mention to the manager.

What I would recommend is putting an O2 sim card in to the phone as Tesco use O2 network just to see if the phone will start up, if not its tesco at fault for giving you wrong information.