Hello and welcome to JustAnswer!
Did the dealer actually do anything to try to diagnose the problem or did they just clear the codes?
There are a few things that can cause this.
It could be a very large leak in the evaporative emissions system. After fueling it will run an intrusive test on the evap system to check for leaks. If it sees a large leak just after you have gotten fuel then it will turn on the gas cap light and set a fault code.
It could be the ESIM or it's wiring. The ESIM is the evaporative system integrity monitor, it's what checks the system for leaks. If the switch in the ESIM fails and doesn't close then this will be perceived as a large leak or general failure in the system. A bad ESIM is the most common cause for a gas cap light when the cap is actually tight, and it's a minor repair. A replacement ESIM here in the US runs $8.
It could be a lack of vacuum to the purge solenoid or a broXXXXX XXXXXne from the engine to the purge solenoid, or a broken/pinched line between the solenoid and the canister. These are possible but not as likely. Most likely you just have a bad ESIM.
You're welcome and good luck with it!