You should troubleshoot it, by walking the line from the inlet to the tank. Check the clean outs, and see if you have water flowing through them. If not, it is before that point. A likely problem if it is stopping up is roots that have grown through a crack in the line.
Septic tanks are fairly simple to understand. The problems is either in the pipe leading to, or the septic tank itself. If the toilet overflows, it needs pumped out.
Find the source of the backup; it may be as simple as a leaking pipe in the basement. Likewise, there could be an inherent problem with the plumbing if the home is new. Next it's time to go outside and observe the area around the septic tank.
First you must check around where your septic tank is located and see if you have any sewage on the top of the ground. The grass will always be greener around your septic tank if there is. Is the tank full if it is need to have it pumped out if it is.