Thanks for your advice! I do try all the steps you say and the single cut plasmid+ligase grows a lot of colonies while single cut plasmid not. The problem is mostly likely the second digestion especially in this case BamH1.
To standardise the ligation reaction one easiest step u can follow is
digest ur plasmid with one of ur enzyme and ligate back in diffrent conditions
and look for colonies .
perform a transformation with these contols
1) uncut plasmid
2) single cut plamid
3) single cut plamid + ligase
this approch at least will allow to check where is the problem??
I am going crazy in this step!!