Sent text not showing as me to my contacts.

Hey guys. 

Just joined Smarty from giffgaff, used a pac code to keep my original number. Transfer went through today. When I call or Watsapp my contracts it's showing as me. When I text, to my contacts it's showing as unknown and the number is the original sim number and not mine that I've imported. Chatted online with an agent and he tried all sorts but wouldn't solve the problem. He ending up saying I needed to order a new sim card! 😳 🤦‍♂️ 

Phone is an android OPPO Find X5 Lite.