I was just able to put an award hold last night for saver J for SFO-SIN-CPT, 1 seat, for October 2019. I mentioned to the agent that I needed some time to transfer my miles from my Chase UR, and at first she extended the deadline to Monday 11/12. When I said that it might take up to a week or so, she ended up extending it to August 2019!
The space from SIN-JNB was very elusive. At first I used the search on the website which showed the saver J available, but when I tried to book it, the agent said the space suddenly disappeared. Fortunately she was able to find saver J space only 2 days before my original date.
I used Skype to dial the Singapore number, and was on hold for only 10 minutes or so. The agent was very helpful, patient, and accommodating.