Why would you need a VPN? A sensible run call centre would be in 2020 using software that runs in a web browser, which will be running https anyway. Best practice is to secure the endpoints because you can't trust the internal network anyway. All you should need is a Chromebook or better.
Then you just need a way to route calls and VoIP does not require a VPN either to be secured. I had to call eBuyer today due to their silly systems ignoring the input address and defaulting to my work address and well the building is closed. I would lay money that the call was handled at home based on the background noise.
If I where in charge I would be on the line to the lawyers looking for grounds to fire the person responsible for call centre operations for failure to make sure staff could work from home. Two years ago it was "beast from the east" so it's not exactly an unprecedented occurrence. There where a couple of bad winters on the trot a decade ago too, so failure to prepare is IMHO gross incompetence.