Hello ewelina20,
Welcome to Apple Support Communities!
I understand from your question that you are wanting to trade in your device and buy a new one. I can certainly help you with this! (and congratulations!! that's super exciting).
I would reach out to Apple Support for your issues with your phone currently before trading it in.
You are able to trade in your device in the purchase process on Apple's website. When you are going through payment it will deduct that off of the price and you will be sent a box where you can send the phone in. If the device is not in the condition told when doing the trade in, the payment method used to buy the new phone will be charged the difference.
You can buy a refurbished device. With the SE generation 2 being so new, I doubt there will be any now but you can check! I have linked the refurbished website below.
Apple Trade In
Apple Certified Refurbished
I hope this is able to resolve your issue. If you have any more questions or this does not resolve your issue, please reach back out on the thread!
Cheers.