You are already on the visa extension, no you can not come back in on the extension. You can come back in on visa exempt 30 days if your country passport allows that or you need to do a visa run and apply for another TR60 visa before returning.
they will be busy because they were shut for Songkran plus their website crashed and so probably got heaps of inquires this week after opening Tuesday. But yes plan B is 30 days exempt and 30 days ext
Thai Sydney consulate website is up and going again, you could go for the TR60 visa with pre-approval online then if you decide you can then extend that when in Thailand giving you 90 days
Pending means pending no guarantee it will be approved, but more than likely it will be as if they were going to decline it you would have got decline quickly