Faulty TFL Oyster and Payments

Had my wallet stolen, so lost my Freedom Pass. Purchased TFL Oyster Card plus £10. Just made 2 short journeys on the train, normal ticket price 3.50 each. Next day went to catch a bus on another short journey, and was rejected, no funds on card. Checked at shop and reader said it was minus £2.80? It seems the Oyster card system can not be trusted. Today I used my Bank card to make another journey on a bus and was only charged 10p? The TFL Oyster Card and payment system is a mess!

Welcome @Rick127

You need to call 0343 222 1234 as this a tech forum.

However, you must have the enough Oyster credit for the most expensive journey - £9.40 peak, £6.40 off peak or £1.75 on a bus - to be able to tap in. Keep within maximum journey times - Transport for London

The 10p on a Contactless is a first-use fee, TfL calculates your daily fee after 4am each day to apply the apply the whole day as a single transaction. This is so the daily cap can be applied.

The bank card issuer is providing you with a credit facility for the whole day.

Use the app TfL Oyster and contactless app - Transport for London if you want to see the details in real time (well up to 30 minutes)

To answer your specific maths question, you must have failed to tap out with one of your £3.50 trips as £10-£3.5-£9.40 = minus £2.90. See Refunds and replacements - Transport for London or go to https://contactless.tfl.gov.uk/ and tell the system where you should have tapped out.

Even when the barriers are open, you must tap BOTH in and out or you will be charged the maximum fare.