Take it back there.
First of all, they said that your car didn't have a tranny dipstick? That's kind of hard to believe. Even if it did, they should have been able to tell if it was full or not. If a mechanic told me he couldn't be sure how full the tranny was, I'd tell him to drain it out, and if there wasn't enough in there, he was giving me a new tranny (Or at least checking for damage). If they couldn't, that's their fault; they shouldn't run a business doing transmission work if they can't tell if it's full of fluid!
Bottom line, take it back, be demanding but keep a cool head as well. Your car isn't shifting right after their service; it's up to them to make right any damage they may have caused.
