"Trickling" or "gas drip" when it's turned off at meter???

Has anyone ever heard of gas trickling out to appliances when it's turned off at the meter? Or a drip, (ie "sometimes the amount that drips through is too small to charge, so these charges only appear every so often when a certain amount of gas has dripped. Gas lines are like water lines, they will send gas to the appliance even if they are turned off. ")?

These are 2 of the, to us, very strange reasons we've been given by Ovo staff for charges on our online gas account being added when our gas is turned off at the meter and all appliances turned off. 2 days ago, for example, there was over 4kWh of such trickles or drips in a one hour period when the gas was off, all appliances were off & we were out of the house (out if a total of 6.5kWh for the whole day!)

We are at our wits end with this, we've been trying to get Ovo to sort this out for around 4 weeks now. We are pensioners, and, to be honest, it's making us ill & we really don't know what to do next. All we want is for someone at Ovo to admit there is something odd going on and to tell us what they can do about it. 

Can anyone advise, or suggest what we should/can do? Our gas is currently turned off apart from when we absolutely have to use it for personal washing (we've found all sorts of wonderful ways to do everything else without gas, even considering using the barbecue instead of the hob 😂)