my car can't climb even a small ramp

Have a mechanic do a compression check with a gauge. It doesn't cost much (about $100 USD here in the USA) and doesn't require any more skill than changing spark plugs. The results will tell you definitively if the engine block needs to be replaced.

The North American version of your car, the Toyota Scion, has had a long history of power/acceleration problems caused by a defective VVT-i controller, which changes cam timing for optimal power. Most of these cases are accompanied by an illuminated Check Engine Light (CEL). The repair is also not expensive, about $100 USD.

Other owners with model years 2007-2012 have reported heavy oil consumption and power loss issues due to defective pistons made by Toyota. There are no reports of a CEL, only low oil light on dashboard. This issue seems to pertain to the 2az-fe engine. Again, a compression check will tell if you have this problem.

If you have changed the transmission fluid (ATF) and the problem has gotten worse, try changing the fluid a least once more. A neglected transmission, after changing the fluid, can suddenly dislodge sludge particles that clog the transmission. Changing the fluid again can often clear the particles and restore transmission performance. You may even have to change the fluid several more times every 1,000 km.