Hello!!
Welcome to the TechnoFino community and thank you for posting here.
Coming to your Question, was the amount debited from your bank account? If yes, then you should have received a transaction id for this payment. Use this transaction id to get in touch with the bank (which you used to pay) and request them for a transaction reversal.
Generally, I have seen that once a transaction is done successfully, it will not get reversed and show in the credit card account in a 48 hour period. UPI transactions generally get updated immediately.
I would suggest that you wait at least for 48 hours for the backend servers to update the transaction status.
Now about the "Pay now" button being enabled again. See, there is a very long chain of entities involved when you fetch your credit card bill. The internet is slow and buggy at times and the bank servers are not in sync most of the time. So, as soon as you pay your bill, it may not be updated immediately everywhere. Therefore, it could be that the app was thinking that the transaction failed and the bill is still unpaid, so you get the button enabled again. Or it could be a simple User Interface bug, we never know!!
In the word of programming and app development, an outsider cannot easily understand the maze of code some developer has to go through to make a simple button work and we are talking about a long chain of events here. So, yes as per my experience, I would conclude it be be a bug and get on with my life.
Once more thing, replies to your first 3 post will be delayed as they will be awaiting moderator approval, but worry not.
Phew!! thats a long post.
Have a great day. Welcome once again and enjoy your stay here.
Thanks!!