OP, your mistake was to use the agent to obtain the Non O based on retirement.
You just needed to him to open bank account (approx 5k)
You can either use agent to obtain 12 month extension and ongoing extensions together with reentry permit. OR
Kill off you non O and when next returning to Thailand start process over.
As pointed out you can obtain the Non O in the UK or simply enter Thailand visa exempt or tourist visa and obtain the Non O at Thai immigration.
You have the bank account so just meet the Financials and no need for agent.