Make sure u cancel yr WP and get NOC from DOL , if u fail to do so and enter again in Thailand in future you hve to pay 20K. So cancel your extension and burn the paperwork bridge completely.
Some cos can get u a Non B here in Bkk itself , but it takes a lot more paperwork. However , it's more easy for cos to send their future employees out of Thailand with paperwork and get it thmselves. Your HR is right , no Non Immi visa is directly converted to other . You need a T visa which will be again changed to Non B inside or outside , depending on cmpny's profile and paperwork.
In my opinion, since you have been denied entry twice , if I were you I would have sit back at home for at least 3 months, first thing. Secondly , I am assuming you lived in Thailand only on T visas for 3 years that means your passport is bleeding with Thai stamps. Dump your current pport and get an METV of 6 months and come again and this time use T visas smartly. Good luck. Cannot tag you , it's for the OP
I am sure your co. HR is too lazy. Get her on 60 days Visa here IN BKK and then go with paperwork to local immigration. You might take help of some agents as well that might get a bit costly but hassle free and believe me it's easy peasy. Good luck
Krishn Menaria I would suggest you using an agent in New Delhi. Google about good / reliable agents with office address and website and apply through them. Thai consulate in New Delhi is quite strict , however , the agents know how to get things done. Honestly I have never seen an Indian retiring in TH. Another option , try Kolkata , the consulate over there is infamous for issuing visa with paybacks. That is one place which I have seen issuing even NON B by back door , let alone NON OA. But , be careful with agents and do full research via face to face sessions with them. Good luck.