Did you enable the Easy Roam feature on your account?

It’s suppose to be activate I receive a text when I arrive in London that it was activate 

Did you use the proper format of +44 and leaving out the 0 in the phone number?

Leaving out like keeping the 00 or remove the 00

So most cellular numbers worldwide have a 0 in the carrier code for the number. You've gotta remove that 0 when you use the +country code to message that number. I'm not sure of the exact number.

I see that 00 is the UK international calling prefix. I don't imagine that 00 would work with a Canadian number to dial out and that you should stick to “+” as the international calling prefixes vary. From Canada/US its 011.

I suggest using “+”  as it's the universal international dialing prefix.

So I suggest dialing, for example, “+ 44 7975 777 666” instead of “00 44 7975 777666” or “00 7975 777666” or wharver you have for the number. If you don't mind, you could post an example of the number you're trying to dial? I'm curious to see exactly what format you have your friends number in. Feel free to use the fake number I've used to do so or just 5’s or whatever.