My reading is that, rather than continue in employment and seek an ill health retirement, all agreed prior to retirement, the OP resigned and then sought to have his pension upgraded on the grounds of ill health and inability to work. It seems to me that, if so, this course of action was unwise as all the leverage had whilst still employed is gone. Having resigned, the option of saying (when refused) "OK, I'll carry on working, but off sick, and let's see where that gets us" is no longer there.
The options for the employer are then:
1. Disciplinary on capability grounds leading to termination or
2. Retirement on ill-health grounds
For an employee with a short tenure then 1. is the more likely scenario but where service of 30 years is the case (OP?) then 2. would be the more probable outcome. But that ship has sailed...