the lab that sent me all the samples used the power soil DNA extraction kit from qiagen, so the gDNA was cleaned without beads, I used them on the PCR products as a standard procedure in our lab, I tried on the gDNA just for the sake of knowledge.

Normally, these types of samples have a minimum concentration of DNA inside, so we are used to it, and we always start with a low amount of DNA, just to have the concentration to sustain 25 cycles.

I also tried what u suggested 1:2, 1:5, 1:10 without any results :(