Support not reachable to expand license

I'm writing here because the support (sales@nextdns.io or education@nextdns.io) has not answered any of my questions yet (since September!!!).

I am the admin of a school and we have a 250 persons/computers educational licence. No we want to expand this licence for further 250 or even more students. In the existing account I haven't found any possibility of adding people/computers/licences and I do not want to create further accounts because in some years we would have appr. 5 accounts, each for 250 students.

I'd like ONE account for these (1250) students.

What shall I do?