If you are a Privilege Club member you will find a number to call for your tier on your dashboard. They should answer more quickly than the general line.

If not then others have reported success contacting them via twitter. You could also try calling offices in another country. If you use Skype or similar it won't cost much. I find Doha always answer quickly.

Or you could raise a new voucher request through their online portal. Speaking to someone may be quicker though.

You have waited a long time and many people complain about the call centres, but to cut them (and all airlines) some slack, they are having to deal with millions of reservation changes each month currently, with some offices still shut globally.

Good luck!