Why is my toilet completely blocked after flushing twice?

The fact that the water just rises back up after intense plunging means the clog is likely much further down the drain than just the toilet trap itself. You are probably dealing with a main line restriction rather than a simple blockage in your toilet's P-trap. Before you do anything more aggressive, try this quick test to narrow down the problem. Go to a sink or a bathtub and run the water for a couple of minutes. If the water starts to back up or bubbles up in the toilet bowl, you have definitively found the issue. That confirms the blockage is in the shared sewer line, not just your individual fixture. If the other fixtures are draining fine, the clog is localized to the toilet and you might try a heavy-duty auger designed for toilets. If the whole house or apartment seems sluggish, it's the main line, and that is almost certainly the property management's responsibility. If the main line is the culprit, trying to push it with a plunger or snake is often futile because the pressure needed is too high and you risk damaging the seals or fixtures further down. If the plumbing fails this main line check, you need to document everything regarding the building's maintenance responsibility and contact the appropriate regulatory body. A small snaking tool or power flush with a professional-grade auger might handle a localized clog, but if the sink also backs up, stop trying to fix it yourself. This is definitely beyond a simple DIY fix.

I totally agree that checking a sink or tub is the smartest first step to see if it's your personal line or a bigger problem. I had a similar situation in a rental when I thought the clog was only the toilet, but it wasn't. We found the actual restriction was deeper in the drain stack, right below the main entry point to the building. It was definitely a main line thing, not just the fixtures.

I had this exact thing happen a few years back and it wasn't the main line at all, which was a relief. It was just a heavy accumulation of grease and hair right at the toilet connection point. I ended up using a pair of those flexible grabbers that are designed to fit in narrow pipes. Seriously, it was the only thing that acutally pulled the blockage out of the U-bend underneath. If the sink test clears, you might need to visually inspect where the toilet drain meets the pipe, because sometimes the 'clog' is just sitting there waiting to be pulled out.

I did try the sink test once but the water seemed to drain normally, which is confusing because my toilet was still completly full. My house has older cast iron piping and I worry about damaging it if I start aggressive snaking. I found a discussion elsewhere mentioning that sometimes slow drains are actually caused by things growing in the line. I am wondering if that kind of root intrusion is somthing people have experienced before in older plumbing setups.