Hey r/banter. Autist here. I need some advice.

So recently I emailed a company about a problem that I had had and they let me know that they fixed it . Should I respond to their email and say "Thank you :)!"? They were being very polite and friendly and I would like to know that I appreciate what they have done. But I don't know if my "thank you" would just be a waste of their time ?
Should I be grateful but not say it or should I waste their time with my gratitude ?