Can I get refund if I didn't use add on travel data.

I think that data is gone :-(
But it might be worth it to contact them just in case.

The travel add are not refundable and that's they will answer you. I know that because the question has been asked in the french side an à Whizz gived this answer.

Unfortunately once you've bought it, if you don't use it, you'll lose it after the following plan renewal.

Fizz support cannot provide refunds for travel add-ons.

Short answer is no. Travel add-ons are good for current billing period and next.
However, funds in your wallet can be transferred back to your payment method.

No refunds for travel add-ons. They will get lost.