Nie znam kontekstu (czy dotyczy to sytuacji obecnej, czy przeszlosci), ale podejrzewam, ze wydarzylo sie to niedawno, tak wiec uzywam pres perf
1. You have written that the box weighs 20 kg, but in reality it weighs only 16.9 kg
2. The box has been opened (i dotarlo otwarte)
The box was opened (nosilo slady otwarcia, ale dostales je zamkniete)
3. Tell me how many books you sent me and how much money you have got left.
4. Make sure that next time the package is better protected.
pzdr