ok man if your into nutrition then you shoudlve figured it out cause your last sentence just gave you the answer
"I am currently in the last phase of "rock-hard challenge" program from M&F magazine. So my diet consists of approx 1800 calories daily (this last phase really restricts the calorie-intake!)."
The answer is to cut down on the cals up protein intake, do lower abdominal crunches eat every 45mins to an hour eat like a nutri grain bar ya kno something that small but whatever u want to keep the metabolism burning quicker than it is dont eat 3 hours before you go to bed and eat 30 mins after waking up! pick up another fat burner if u liked lipo6x then get that or others that i used to cut down to get my washboard abs, were methly ripped, lipo-6, hot rox and ephedrine if you have somewhere by you that you can actually buy it from. thats my best advice man if you do that then you will lose the last few ibs so if your at 1800 cals eat only 1700 the next day and then 1600 then next dont go lower than 1600!!! unless your body really isnt burning the fat but if you did a cycle to bulk up or w.e make sure you lift hard still even with less cals man ok? u got it u can do it!