Is it possible to have two phone numbers on one phone?

You should definitely contact your carrier about this. They might be able to transfer your old number to your new SIM or help you understand what's happening with the numbers. If you still have your old SIM, using that in your new phone could also be an option, but it's best to check with them first.

When you get a new SIM card, you usually receive a new phone number unless your carrier makes a change. If your old number is still ringing through to your new phone, it could be because your provider is forwarding calls from your old number to the new one. It's not extremely common, but it can happen! To clarify what's going on, I recommend reaching out to your phone carrier to get all the details sorted out.