Hello @Acexbr ,
Welcome to the community,
You can either log-in via the My EE App or via the website . With My EE App, click the top right, then click settings and then Device and Sim, you should be able to do it there.
To contact EE customer service dial 150 from your mobile phone or ring customer service for free using Skype or another phone: +44 800 079 8586 or +44 800 956 6000.
