Not really applicable to Linux kernel bugs, but I have a story of it being much harder than one would expect to convince my ISP (a generally cool company, as op

Not really applicable to Linux kernel bugs, but I have a story of it being much harder than one would expect to convince my ISP (a generally cool company, as opposed to some behemoth telecom) that their payment system would allow me to pay them essentially nothing, but their system recorded it as a payment in full. I pay my ISP using a method where I use an app on my phone to scan a QR code and I can then pay with my credit card (and get associated rewards). For reasons of maximising my rewards, I decided one month to try split the payment and pay a small part with one credit card, and the remainder with a different one. I opened the app, scanned the QR code, changed the default payment amount to about 10%. A moment later their system says “Thank you, paid in full!”. I send customer service an email explaining that there is a flaw in their system which has allowed me to me to underpay. Them: “Don’t worry, we can see you’ve paid us.” I reply: “I really haven’t, you need to escalate this to someone technical over there to investigate this further.” Them: “I can confirm you’ve paid.” Fortunately for my ISP, I’m a good person and they have a presence on a local forum, I PM’d one of the reps on there who based on their posts was possibly one of the founders. And he responds saying something to the effect of “thank you very much, I have no idea why customer service didn’t escalate this” and goes on to explain that the payment app evidently did not respect a flag in the QR code which should prevent me from editing the payment amount and he had fixed their code to actually check the incoming amount. Same rep a few years later was able to resolve unstable Spotify streaming issue I reported by getting Akamai to fix their DNS resolution to use the PoP on my ISPs network as opposed to the one on a different ISPs network which was throttling their peering link.