Something isn't right. For you to be on COBRA, you shouldn't have an employer. COBRA in this context refers to continuation coverage for employees who leave an employer. In other words, if you still have an employer, you aren't eligible for COBRA. But if you are eligible for COBRA, your former employer wouldn't even be involved. You'd be dealing with that program, not your ex-employer.
So it's not clear to me what's really going on here. It sounds like you're out on leave of some sort, and your employer doesn't want to keep you on their group health plan. This sounds more like an FMLA issue than a COBRA issue. But FMLA is complicated enough to make contacting a local employment attorney worth doing. It may be that your employer is under no obligation to keep you on their plan, in which case taking your checks is problematic. On the other hand, you may be entitled to remain on the plan, in which case cancelling your coverage is problematic.
Regardless, something doesn't add up. Contact a local attorney.
This answer does not constitute legal advice and does not establish an attorney-client relationship.