How does C2 trade expired vix options?

My system: MCProTrader has just experienced a huge loss due to the error of C2’s handle of vix options. The May Vix settlement value is 12.98. So the options of vix 13 call, 14 call and 15 call should all expire at 0. But C2 does not use the correct settlement value to close vix options. Anyone from C2 please explain. It is not very professional that C2 offers vix options trading but does not follow the correct way to settle them. Have any system providers who trade vix options also experienced this issue?

MC -

I have corrected the price at which your volatility options were marked as expired by C2 in your Model Account.