Call ETS ASAP! We had an issue last year, where no proctors had shown up to the room we were supposed to be testing at. After talking with ETS that morning we were given the option to a make up test, we just had to agree as a whole group which weekend to take it. However about an hour and half after the supposed start time one of the proctors showed up and we went ahead with testing and didn't have to deal with a make up. The option for a make up test should be possible if ETS made an error about testing location.
There's almost no way they reschedule the test. Unfortunately, that would compromise test integrity. You have a strong right to complain, however, and it's possible that schools in the US will still look at your application and offer preliminary acceptance based on your performance on the April test if you include a corroborated statement about ETS's mistake with your application. Getting ETS to send an apology letter to the schools you've applied to might be best case scenario.