Toyota unable to fix my car

Take my 2014 Toyota avanza 1,5 to a Toyota dealership on 31/01/2019 cause car has no power. After changing fuel pump and filter and the cleaning of petrol tank same problem. After a lot of test they figure out that the computer box is faulty. After changing computer box the problem stay the same.Now they say that they can't/don't know where the problem lies.Help me please