DNO refuses my G99 application

So I've had emails back from my dno, they tell me I can not connect my single phase 8kw battery inverter to the grid (a Victron multiplus ii 10kva inverter) unless I have 3phase installed. I can however export 3.6kw with my current solar inverter. So I asked if I need 3 inverters, one for each phase, and I'm told no, I only need to connect my 8kw inverter onto one phase. The argument is that the voltage will rise if I connect it to my current single phase which is a part of the 3 phases on the utility pole, so how can extending the 3 phases to the house, and still only using 1 phase sort this voltage rise issue they claim which i think is b.s. My inverter produces 230v, my grid is more like 240v, so how can the voltage rise? Current yes but voltage?

So I've had emails back from my dno, they tell me I can not connect my single phase 8kw battery inverter to the grid (a Victron multiplus ii 10kva inverter) unless I have 3phase installed. I can however export 3.6kw with my current solar inverter. So I asked if I need 3 inverters, one for each phase, and I'm told no, I only need to connect my 8kw inverter onto one phase. The argument is that the voltage will rise if I connect it to my current single phase which is a part of the 3 phases on the utility pole, so how can extending the 3 phases to the house, and still only using 1 phase sort this voltage rise issue they claim which i think is b.s. My inverter produces 230v, my grid is more like 240v, so how can the voltage rise? Current yes but voltage?