Sometimes you have to reset configuration to defaults to be able to access the device after upgrade if just one more reboot isn't enough to re-gain access. If you haven't done an export or backup of the configuration before the upgrade and haven't stored it on the flash on the device (which survives a reset to defaults), and you would prefer not to lose the existing configuration, there is still hope.
First, set your PC's IP address so that it was not
in Mikrotik's subnet and try to tell WinBox to use the MAC address of the Mikrotik rather than its IP address.
Then, try to access the Mikrotik via its IP address - in this case your PC must be in the same IP subnet, so either it must get its IP address from the Mikrotik or you have to manually configure it into the same subnet.
Both the above methods depend on the configuration before the upgrade and on how it was converted into the format used by 6.44.3 (both IP and MAC access by WinBox may be blocked in the configuration), so both may fail. But if your Mikrotik has a serial port or a USB port, you may still be able to connect that way. If your PC doesn't have a serial port, you'll need one USB-to-serial adaptor for it, and if the Mikrotik only has a USB port, you'll need a USB-to-serial adaptor for the Mikrotik. Then, connect the two serial ports using a "null modem" cable (5-5, 2-3, 3-2 in case of 9-pin connectors at both ends) and use PuTTY or some other terminal software capable of using serial ports to connect. The serial settings are no parity, 8 bits, 1 stop bit, 115200 bps. Connect, press Enter, the Mikrotik should respond with
MikroTik 6.44.3 (stable)
If it does, use your normal username and password to get in and check and fix what is wrong in the configuration.
Instead of writing novels, post /export hide-sensitive. Use find&replace in your favourite text editor to systematically replace all occurrences of each public IP address potentially identifying you by a distinctive pattern such as my.public.ip.1.