Just get it refunded. Smartthings is primarily a cloud-based system. You can’t even change the mode without access to the smartthings cloud.
Hubitat is a tiny company founded by some former smartthings power users which does operate entirely locally except for some third-party integrations like voice assistants. They have had a lot of success over the last two years, and even if the company went out of business, because it is not cloud-based whatever you already had set up would continue to function. so I would recommend taking a look at that.
It doesn’t have a nice app like smartthings does, but you can add the third-party SharpTools for that. 
There are other mostly local options as well, see the following thread for more discussion: