Reliance Jiofi 3 device ( wi-fi router) showing extra data consumption

If the JioFi is in near vicinity of the VOLTE tower, then it is likely to download the content at the higher speed. So for example lets say with 2G mobile you get speed of around 64kbps. With JioFi in VOLTE region would give you around 264kbps to 1mbps. This loading speed surely burns the data at much higher speed than the regular data consumption. So your 1MB page load at the speed of 500kbps maybe leading to more data burn. This often is the case with data consumption. However if your speed is low and also the data consumption shows higher then it seems like the issue is with the way JioFi is taking more data to retain the connection with the nearby tower. So that consumption end up costing more burn of data. In that case definitely contact the support of Jio and ask them how to resolve this. Though they seem to be lacking on the technical support side, I am sure they'd be able to fix your problem. Make sure to keep the background services to low if possible. Faster downloads through JioFi burns up more data. So you're left with the slow speed at 128kbps later. So this is an expected behavior.