What should I do if I received a wrong immigration stamp in Thailand after switching from a retirement extension to a non-B work visa?

I have been in Thailand on an extension of stay based on retirement valid until 8th October 2019 and was recently offered a job. I took all the documents to Kuala Lumpur, and applied for and received a single entry non-B work visa on 7th June. I reentered the country at Suvarnabhumi on the same day and was told that there was a mistake and that I should have cancelled my retirement extension first. Information on Thai Visa Forum however suggests though that this is automatically cancelled when you leave the country and get another type of visa. Anyway, after a bit of discussion, the immigration officer took me aside, changed some entries in the computer system and stamped me in until 4th September on the non-B. So far, so good and I now had to wait until I could apply for the full extension.

On 19th June, I went abroad again after having obtained a single use reentry permit, again at Suvarnabhumi. On returning to Bangkok on 1st July, the immigration officer overlooked the non-B and single reentry permit and stamped me in on the retirement reentry again, until 8th October. Unfortunately, I didn't notice this until yesterday, where I had to apply for the work permit and extension. In theory, my retirement extension has been cancelled both by getting a non-B and by the original entry as a non-B on 7th June. My non-B stamp is marked as used and I'm currently stamped in as NON-RE until 8th October. Can I go to Suvarnabhumi somehow and get this changed, or do I need to go to Chaengwattana? If so, is there an immigration office this side of security? Or will I have to fly out to KL again to do another non-B? Anyone else had this experience?