The UMP45 Is a 34Damage Maximum weapon(highest pers hot of any PDW) the 34Max damage begins to drop off at 8meters it begins to drop by 1DMG per 2 meters of distance reaching its minimal potential damage at 40Meters at 12DMG per shot. Even if you landed a headshot at point blank 34x2=68, it would not be enough to kill the anyone or anything  in 1 shot . I would have been inclined to believe your story, if you did not try to tell me bout your "UPGRADED" UMP45. Due latency+high ROF weapons like the FAMAS, AEK,P90,  MP7 can be mistaken for one shot kill hacks, The UMP45 is a 600RPM weapon with a muzzle velocity of 320MS It can not give out the 1shot impression(The Aug A3 ,for example has a suppressed muzzle velocity of 335, once cut in half it is still higher than the UMP's).
With all the information and technical data in place I have but one conclusion to make, Our admins acted in compliance with server protocol, If you wish to get unbaned post in our unbans section.

There you go the fairest of reasoning you could hope for