I only get a engaged tone and then says call rejected but the sim works in my other phone how can i sort this

The phone may be SIM locked, that means you can use it with a SIM card purchased together with the phone only. This mechanism protects phone service providers (PSP) business model from people that enter mobile phone contracts with a discount phone from just changing the SIM card for a cheap prepaid competitors SIM.
A second (but not necessarily intended) effect is, stolen phones are rendered useless to the thief.
If you provide proof of ownership to the PSP and the lock-in contract is fulfilled (usually two years after purchase), most PSPs unlock the phone for free or for a small fee.