Fly from Cape Town to England and return to another province

Have a good day,

I am planning a trip to England to visit my family and I will be flying from Cape Town. I wish to fly from Cape Town to England, then from England to Durban, but I do not wish to buy 2 one way tickets as this costs a lot more than a round trip ticket. Does anyone know if it is possible to do it at a price lower than 2 one-way tickets.

Thank you.