Cannot pay bounced payment

Hello, for the last 3 attempts the payment for my internet has bounced back. I’m unsure as to how to pay the outstanding balance since the app says I don’t have anything to charge. This morning I got an email from Xfinity stating I had a payment return fee. What exactly should I do? I’ve tried to call and the AI doesn’t know how to help me fix this. All I wanna do is pay the bill