the wording on their own statement (Thai Embassy Vientiane) is wrong, what they mean is that they will issue only one ED visa from a language school covering the period of one year, means the OP can apply a new ED visa in August 2019 only. If he apply a ED visa from an University it will be no problem.
at the moment I would say avoid both places for the time being. If you have option to fly to Myanmar, KL, Hanoi or HCMC and fullfill requirement I would do. Or make a good planning for Vientiane, now you can book for 17th, 18th and 22nd April.
another reason was that their system identified some mail account as fake and despite confirmed booked they were refused. I had one customer. That should be a thing of the past.
There was, last week, a scam exposed on various Filipino Facebook sides involving a Company in Bangkok that cooperated with a company in Phuket to obtain fraudulent Non B, so they check documents and they also check with airline about the booking of flight. If you plan to use our service, please make sure that all in order. Savannakhet is aware of these things.