We had a similar struggle here. Tried the reward system but she would only go when rewarded. Eventually I had to ditch pullups altogether. She went no bottoms during the day and panties at night. With no bottoms she always went to the potty. As soon as she had panties, she'd have an accident. It went on like that for a while and eventually we put her in panties and we set a timer and told her it was non negotiable. Every 30 minutes she went to the potty whether she had to or not, and she had to sit for 2 minutes unless she peed then she could get up immediately. After she was dry for a while we increased the time. Everytime she peed or pooped we danced and sang, "I'm so proud of KID NAME!" And we made her sing it to, saying she was so proud of herself. Eventually she started believing it, she would go to the potty on her own and then dance and say how proud she was of herself. We'd still dance too, but after a while she didn't need us to dance anymore. Eventually she didn't need to any more, although she still does when she has a poop.

It was not easy and it was not quick, but eventually we did get there. Some kids don't pick it up quickly and need more time. Our kid needed it to be more structured for it to work. She works better that way, and so do I. Good luck, you will get there.