I know it's an old question, but I'm going to go against the advice in all the other answers.
I am 6ft and currently weighing 83Kgs.
Fat distribution and muscularity will make a big difference here, not so much the weight on the scale. I've been 72Kg at around both 20% and 12% body fat and didn't have a visible 6-pack on either (I started seeing some lines at 10%). My coach was around 80Kg at ~12% BF with very visible abs. We both have the same height.
...managed to lose 13kgs with running, gym and rollerblading and skating.
The more you do cardio, the less calories your body will burn for the same effort. So you'll need to do more cardio to burn more calories. How far do you think you can go to keep burning more calories?
On the other end, you can always lower your calories. The problem is: your body will also get used to have less calories, and will start burning less over time. So how low do you think you can go with calories without starving yourself and being unhealthy / miserable?
What I'd suggest instead is: focus on building muscle. More muscle requires more energy, burning more calories. So you will need to eat MORE to maintain or increase your lean body mass.
More muscle also has another benefit: you can have visible abs with a higher body fat percentage, once your abs are developed enough.
So my advice is to focus on resistance training at the gym (weight lifting) to create a muscle building stimulus that will make your body burn more calories, so you can have your junk food sparingly (I'd say 80/20, meaning eat whole foods 80% of the time).
Spread your calories during the week, so you can eat more on some days and compensate on others. Even if you get into a calorie deficit it will not going to be so extreme as 1200kCal / day. You don't need to work out more on the day you eat more, just make sure you don't exceed your weekly calories.
You should find what are your daily calorie needs or TDEE (Total Daily Energy Expenditure) using the calculators linked. From there you can figure out how much you need to eat to lose or gain weight. Eat more protein and carbs, less fat. Track what you eat for a few months so you learn to gauge how much you're eating.
It's what I learned, what I did and what I see many people I know also getting results with it.