Hello @Hannahcleghorn ,
Welcome to the community,
You should have just continued using your old SIM card, there was no need to use the new SIM card if the old one was working. I would suggest speaking to customer service, if you cannot activate the SIM card yourself.
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.
