Was offered a PhD position, I accepted it but no replies afterwards from the potential supervisors
I don't think you have any reason to worry. Under the current strain and disruption of the pandemic people aren't able to do the things they would normally do. A couple of weeks isn't very long after a deadline as there are probably quite a few administrative tasks that seem to them to be more important to them than reassuring students. The professor in question might have additional issues preventing them from responding in a timely manner (or at all, if they are ill or caring for a family member). 

Assume that all is well. You've done what was required of you. 

Don't keep hammering, though, as it just makes their workload worse. 

On the other hand, you are due an acknowledgement that all is well. A once-a-week email is probably appropriate until you get confirmation. 

Note that normal phone numbers aren't being answered at some places. Buildings are locked and people are forbidden to enter, even to retrieve personal effects. 



You could, however, keep abreast of any news pertaining to that university by doing web searches. There is a lot of disruption and universities are planning how to finish out this year and finding ways to be flexible for next. Bad things are happening. They could continue to happen.