The problem is in order to start losing weight, keep losing weight and then keep it off, the changes you make need to be sustainable. Things like fast 800, low carb boot camp etc are fads which are not sustainable because they're extreme / hard / not good for you. As you've found, they'll get you started but they won't get you to your goal weight.
You need to make healthy, long-term, sustainable changes to the way you eat. Forget "diets", just think about being healthy. Be mindful of what you eat. Eat healthily, cut down processed foods.
I'd suggest the following:
For breakfast - eggs and toast, porridge, fruit, or yoghurt.
For lunch - homemade sandwiches, wraps, salads, jacket potatoes, or soups
Dinners - protein (chicken, salmon, steak) with plenty of vegetables / salad, stir frys, homemade pastas, homemade curries. Basically anything that's not highly processed, and make sure the bulk is usually vegetables, greens, or salad.
You need to fill up on foods that aren't calorie dense, like fruit, vegetables, greens etc, while maintaining a varied diet elsewhere so that you're getting all the nutrition you need. Natural fats in things like full fat milk or butter aren't bad for you.
In all cases, watch your portion size. Stick to two sausages instead of three. Two sandwiches (two normal slices of bread) instead of three or four.
You can still have things like pizza, chocolate and all the other stuff - there's no need to cut them out entirely! But think about how much you're eating that compared to how much you're eating fresh vegetables, for example.
Above all, don't expect changes overnight. The weight didn't appear that quickly and it will take time to come off. The important thing is that it comes off slowly, because that is what's sustainable.