Iphone not able to merge calls

Does your network provider support this feature and is it enabled on your account with them?

Contact them to find out.

How would you contact them

I would call the contact telephone number provided by them. I would assume you can get this off their website, or on the monthly bills they send you.

would it be easier to just move provider?

No. If you are on a contract you can't even consider moving providers until your contract is over. And it's much easier just to call them and ask.

Call 150 from your orange phone.

OK. Pay as you go is 450.