Cubot Quest Dual Sim Configuration Problems

I currently live in Spain and bought the phone in Sept 2019 from Amazon UK. Until now it has been used only with WiFi pending obtaining a nano sim from O2 on visit back to UK. Now I have been trying to install my Spanish Sim + O2 sim with no success. I have carried out a factory reset and still the problem. Both these sims work together perfectly in dual sim phones I have – a BQ Android One and an old Moto G. Problems seem to vary with no data connection, at times network unavailable and at no time both sims active. At one point the phone operating language changed to Spanish! Is there a common issue with phone sharing one card slot that can accommodate 2xNano Sims or 1XNano Sim +SD Card? My current phones have independent slots. Thanks