Not a fix, the website is hilariously unreliable (but so are all airline websites, I think), but when I need to call the PSL from abroad, I use the Skype app on my phone, it costs a few cents a minute.

For what it‘s worth, I once had an award show up that I couldn‘t book through the website, the price would always jump up after getting an error. Since the PSL got the same error they booked at the higher rate and reimbursed me the difference. Might be a solution for you as well.