Welcome to entrepreneurship. Dealing with humans is difficult in general. Plus you are dealing with some pissed off customers. Even harder. This is what you can try -

1. See things from customers POV.

2. Maybe you’re not willing to accept what is built is not perfect & have issues. Once you're self aware it will help manage issues better. You need to move from denial to acceptance phase.

3. Our brains are wired to be defensive. Try to acknowledge or trigger whenever you’re defensive. Hard to explain but it’s like anytime you get defensive an inner force tells you YOU ARE BEING DEFENSIVE.

4. Best way to deal with an angry customer is just to agree with them initially, this will calm them a little & from there you can have a more productive conversation.

Good luck!