Sims 4 DLC is not refundable! But it SHOULD be.
If someone wants a refund within 24 hours of buying one of your games, they should be able to get one.
Forum Discussion
You could try Twitter if you have an account there. You can send a direct message as well as tweet to EA Help.
https://twitter.com/EAHelp
https://twitter.com/EAHelp
