Just use the upper heat and lower heat to pre-heat the oven (or don’t use the top heat at all if you think you may forget to turn it off), then use only the lower heat to bake the cake. You may want to buy an oven thermometer to check your oven temperature.
I had a stove once with both settings—upper and lower. The very first time I baked a cake in it, I didn’t know to turn off the top heat, and, needless to say, the top of the cake was extra baked. I sliced off the top and slathered it with frosting. My sister-in-law still talks about their lovely wedding cake. Lucky for me that it was a very informal wedding.