Very good question, Toni, but I'm guessing they mean the northern summer. Looking them up on the website of our Better Business Bureau, they give the MacKiev contact info as:
Boston, MA 02109-1202
https://www.mackiev.com/
(617) 227-6681
In other words they're here, in the state of Massachusetts, where summer will begin on 21 June. Might be useful to remind them, though, that they have customers in the southern hemisphere and should phrase their communications accordingly.