This is an issue I've had to come to terms with myself. I spent most of my catering life spoilt by having a massive fan assisted electric ovens with space for 24 trays at once. Then one day I left it all behind to work in a tiny 2 chef kitchen where all we had was a bottom heated gas oven. The first 6 months was a nightmare. It's still not easy even to this day but I'll share a couple of tricks me and my colleague have found.
Its all about the airflow:
Forget about the middle shelf for baking it's useless. It's there for roast joints and ... Stuff. Get your baked goods on the top shelf. The reason you are not getting browned tops is all the heat is hitting the bottom of your tray, by the time it reaches the top of your oven and bounces back down to your food it's nowhere near the temperature required.
In order to help cushion the bottoms of your food and direct the heat towards the top, you need to put a tray slightly larger than the tray you are cooking on, on the shelf below. You can add water to this tray for bread and Yorkshire puddings as the steam helps regulate the heat also, but when cooking pastries I find it makes the pastry more likely to split and crack.
Locate the thermostat in your oven. In ours, it's at the top right, in the middle. Always ensure there is sufficient space around it for the heat to hit it. If it's blocked in any way you'll find the oven just keeps pumping heat out. It'll be 300c at the bottom but the thermostat will still think it 100c.
Sometimes you will find the tops are now cooking perfectly but the bottoms are a little less done. At that point, you will be safe to either move the food down a shelf to help crisp the bottoms or if making scones you can safely flip them over just to finish off.
Good luck.
I'm a person that goes on vacation and bakes bread. As such, I have met a few terrible ovens around the world, and temporarily improved most of them to work better...
Grab a roll of aluminum foil (heavy duty is nice if you have it, or if you don't have any are are buying a roll with this in mind.)
On the bottom oven shelf, come in a few wires from the sidewalls (to allow some air circulation) and crimp on one end of a long sheet of foil - this sheet will be shiny side down, hung below the shelf, and attached to the shelf again in a similar location on the far side of the oven. You'll probably need two sheets (one for the front, one for the back) and should leave a similar small gap at front and back for some circulation, while keeping the centers tight or overlapped.
You can get much of the effect (but not quite as well, or as "semi=permanently") by putting foil, shiny-side down, on the bottom of your baking pans. If either is is not enough by itself, do both. It should help a lot.
Best Answer
You're baking using a convection fan. This generally won't work unless the cake recipe is calibrated for it; you'll end up with a cake which is brown on the outside and raw in the middle (as you did). It's remotely possible that a combination of lowering the temperature and convection would be successful, but I don't have a formula for you.
Suggestions:
If the issue with top heat is that the cake is burning on top before the bottom is done, I would suggest placing a rack above the one the cake sits on, and a cookie sheet on that rack. This will protect the top of the cake from the radiant heat of the element, causing it to cook only from reflected heat off the sides of the oven. This may, however, increase cooking times somewhat so make sure to check cake doneness with a skewer.
Or: Add a baking stone on the rack holding the cake as well (under it), and preheat the stone for 30 min before baking the cake. This will give it some heat from the bottom.
Or: both of the above.
Or: get a new oven. They make fairly nice countertop ovens now which have a bottom baking element.