Not a good time
If you are a supplier, and you want me to believe you have the FIRST CLUE about dealing with education customers, there is one rule you must master above all others.
NEVER CALL IN THE FIRST TWO WEEKS OF SEPTEMBER.
If anyone in a school needs something from you, they will call. They will call because if they need it now, this close to the start of term, they are utterly desperate for it.
If they don’t need anything, then you can be damn sure they don’t even have 30 seconds spare to talk to you. It will be this way until at least the middle of the month. Don’t call. Don’t email. Don’t even think about it. I, for one, am far too busy to even feign tolerance if you do.