I don't believe you, but just in case you're telling the truth...
It isn't your ex husband's responsibility to unblock a toilet.
Caustic soda will dissolve toilet paper, faeces and fat. Pour a pack into the toilet and simply wait for a week. You've, apparently, been living like this since November, so another week won't hurt. That will resolve any blockages in the toilet area. I think it would also dissolve a drain blockage given enough time and a strong enough concentration of caustic soda, but you might be looking at weeks for the chemicals to slowly eat through 20 metres of blockage.
If the main household drain is blocked, you need to lift the drain cover and use rods to unblock it. Don't attach any tools to the rods because they can disconnect from the tip and get lodged in the drain. This would be a disaster! It is important that you only twist the rods clockwise to avoid them coming undone and separating inside the drain. This would also be an expensive disaster.
The technique with rods, is to push the blockage up the pipe. If you can get it to move 30cm, it will usually start moving with a lot of speed/force and clear the blockage. You never push down because it simply compacts the blockage and makes it worse. A major drain blockage can require a lot of physical strength to push back up the pipe. This is due to the weight of water trapped behind the blockage - 100 litres equals 100kg.
When you clear a major blockage you will see faeces/fat/sludge blast down the drain pipe at high speed. If you see it slowly passing down the drain, it's probably still partially blocked. You'll need to rod again and, if you can't feel a blockage, apply caustic soda via the toilet (single flush) and avoid using the taps and toilet for a few days. There could be a fat burg that only chemicals or jet washing can remove.
As a previous poster suggested, you probably need to knock on your neighbours doors or go on Nextdoor to ask to borrow some rods and also ask for help.