Overheating when driving is normally caused by a restriction or poor flow. This is normally caused by a thermostat issue or some other restriction. How have you confirmed the thermostat is opening?
https://www.2carpros.com/articles/how-an-engine-thermostat-works
When you say the heat doesn't work, is this a new issue? If so you most likely have an air pocket in the heater core causing the coolant to not flow sufficiently.
I would suggest using a spill free funnel to fill the system and jack up the front end so that the coolant fill funnel is the highest point. This will help work any air to the highest point. This will help force out any air pockets.
Let's start with this and we can go from there. Thanks
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Sunday, September 20th, 2020 AT 2:33 PM