Some corrections:
1. The inspection device cannot know how much money in your account. It would have indicated that your card issuer declined a transaction or that you are on the blacklist for other reasons. Based on everything else said, it is clear that your card was declined by your issuer and this is usually for only limited reasons, either the card is lost/stolen or there isn't enough funds to cover.
2. The worn chip on your card will have no impact on the contactless functionality at all.
3. Given that you are able to resolve the issue yourself on the website, this means 100% that it is your bank which declined the transaction and TfL will not be able to tell you why, the advice you will be given is to phone your bank if you want to know why the transaction was declined.
4. For a bus user, even with a declined transaction, TfL usually still gets paid (there are limited circumstances where they don't), so it's very likely that you don't owe TfL any money. TfL simply acted on your bank's instruction which was to deny you from further travel as you would not have sufficient funds to continue travelling. (When you resolve your issue with TfL, they will just do a check to make sure that you have sufficient funds for future travel and that your card is not marked as lost or stolen, rather than take money - this is if you owe them nothing).
5. The failed collection was definitely not from the tap in on that bus as one person alluded to - it would have been from a previous transaction. The card must have been not good for travel before tapping on. If the tap resulted in a transaction which was declined, the revenue inspection device would have seen it as a pass.
Just a few corrections to that:
1. The Revenue Inspection Device (RID) used to check contactless cards does not technically know whether a card is declined. The validity of a card is determined using a binary of whether the card is on the list of those Not Authorised For Travel (NAFT) or not. A declined payment is not necessarily a direct tally with a card not being valid, as bizarre as that might sound. The list of cards Not Authorised For Travel is fetched by the RID at set intervals when logged on, during the time that the RID is within an area with phone data signal (and if it misses a scheduled update, the RID will inform and prompt the user). With bus inspections, phone signal will usually be retained most of the time.
2. The worn chip can be an indicator that some cards have also been damaged in other ways. I have found that in about 50% of cases where a card cannot be read at all, the worn chip is one of a number of symptoms which indicate that the card is too damaged to be used for contactless payment.
3. Resolving an issue on the website can be done for a variety of issues either with the user's use of the card, TfL equipment not working, or an issue with the bank. Often, TfL will no longer authorise use of a card due to multiple incomplete journeys. This can sometimes, from experience, be resolved on the website; this is a TfL matter and not the concern of the bank in any way, provided there are funds to pay the fare charged by TfL.
4. This depends somewhat on the sequence of travel events. The first bus touch-in which takes your account balance negative will still allow travel. Subsequent touch-in attempts may not, because TfL do not want to lose money to accounts which now owe them "something".
5. The revenue inspection would not know about the transaction with a contactless card, only the card's status in the NAFT list. So long as the card is not on the NAFT list, it should show either a green tick or (if its validity cannot be determined) the yellow alert screen. Of course, if the card became NAFT after the touch-in on the bus, and the list of NAFT cards was updated between the touch-in and inspection, there could be issues where the card may appear to have touched in correctly, but the payment was declined and the card became invalid for further use. The sequence of these events could be compared by using TfL Customer Services assistance, the updated records on the TfL online portal at the end of the day, and the details held by the card issuer.