My last day of employment was 8-21-09. I elected dental cobra and paid 18 individual premiums to cover me for 18 months from 9-01-09 – 2-28-11. I had dental treatment in February, 2011 and monitored my dental coverage through most of March waiting to see when to claim was paid. During this time, the plan still showed active dental coverage. The claim was not paid during March & after that I didn't check for awhile. The next time I checked was May 31, 2011. It showed that my plan terminated on 1-31-2011, a month short of 18 months.
I contacted my former employer who contacted their benefits administrator. They said that because it had been such a long time since the insurance termed, that I would need to supply all 18 canceled checks. I downloaded them and e-mailed the office manager that I had them. She said that now the benefits administrator said that it may be too late to extend the coverage another month and they don't usually retro past 60 days and there is a possibility that it would not retro back and I would simply be issued a refund check for one month of premium. In checking with the insurance company, the coverage was retro termed on 3-31-11 for 1-31-11. This was their error, not mine. Can they really do this? I didn't do anything wrong; why should I be penalized for their error?

If you have the Cobra info and proof of payment, no they can not merely cancel it early without a proven valid reason.

So if they don't pay, you pay for the treatment and sue them.