The Chicago stock option exchange board decided 3 months ago that once ZN went to OTC market, they were not going to allow "NEW" selling of options/either naked or new covered calls. They are only allowing current option holders the ability to buy to close of existing long positions or sold covered calls. Basically we are in a one-sided crappy option market...
If you purchased calls I would hold them as they are like GOLDEN as once you sell to close, you are out of the option game :)