Lots of info, thanks Emmzz. And don't worry, you aren't stupid. Anyone would think that the tank manufacturer should know what they are doing but unfortunately, as you are discovering, this isn't actually the case.
At least your filter has sponge, I was afraid it was one of those awful filters with nothing but carbon and zeolite.
I have googled Aqua Flow 100 and it appears to be a Superfish brand. It would appear that you can remove the media from the media box and that is like an outer cube of sponge with carbon granules inside - is that right?
If it is, take the filter box off of the filter, remove the media and empty out the carbon granules. Then try to stuff as much of the old sponge as possible into the hole where the carbon is supposed to be. Cut it up if necessary to make it fit. Provided the old sponge is even a hint of damp the bacteria in it should be OK.
If absolutely necessary, carefully break the outer casing of the changeable box in some way that you can put it back together.
Instead of changing the media, all you need to do now is squeeze the sponge in some of the water you take out when you do a water change - never clean it under the tap or the chlorine in the water will harm the bacteria colonies. Don't scrub the sponge to make it look sparkly new, just enough to get rid of the debris that will collect in it.
You only need to change the sponge when it literally falls apart. They last for years. Maybe not quite decades, but certainly a
lot longer than a few months.
Until you know if you have ammonia in the water, and how high it is, you'll need to do a 50% water change every day. But as soon as you know the ammonia level, post it here and we can take it from there.
Nitrite is zero, which is good, though if you do have ammonia you will find that you'll get nitrite before long.
Nitrate depends to a large extent on what is in the water supply. If you test your tap water, that will tell you if the amount in the tank is all from there or if you have some bacteria in the tank turning the ammonia into nitrite and on into nitrate.
And some reading for you. We are assuming that you are stuck with doing a fish-in cycle.
This explains what is happening and what you need to do. Sit down with a cup of tea/glass of wine and you'll see what to do.