You need to sim swap from your old sim Guide: Sim Swap: a mini guide 2017 update
Have you followed the steps in the link to swap from your old sim?
If so reboot the new sim until it comes online.
Text the word SWAP to 20220 from your old sim card.
You will get step by step instructions via text message.
I did that, spoke to a customer service agent who organised sending me the new sim but don't think it's been registered, when I received the delivery note it dosen't have any reference to my phone it's blank. wondering whether the agent should have registered at there end.
All new sims are blank.
You need to follow the advice given to activate it.