Just got off the phone with PSL and received two voucher (one for each ticket). It took a mere three minutes.
This was after waiting for a response for eight weeks and multiple contact requests through phone, Twitter and Facebook. All giving very conflicting information or no information at all.
The very helpful lady on the phone explained some things to me: it seems that if you have an outstanding refund (not voucher) request it will go on a big pile and get rejected automatically in 90% of the cases. Then it will go on another (huge) pile of refund requests a special team has to go through manually. That's why some requests take longer than others, which can - indeed - take up to one year to proces. Another thing that has changed is the validity of the voucher(s): she explained that the vouchers are now valid through December 31st, 2021.
I understand that is again just one PSL phone operator and that everyone's mileage (pun intended) may vary and that sometimes not the most correct information is given. I'm just glad I finally got my vouchers after waiting so long and getting all kinds of conflicting information.