Can't get iPad to go into recovery mode to factory reset.

Trying to factory reset my iPad Pro because I locked myself out of it, and I haven't been able to get it into recovery mode. I have researched a lot of different ways and tried using 4 different computer systems to force it into recovery mode and reset it but nothing works. I got it to go into it one time, was able to use iTunes to reset it a little but in the middle of resetting it kicked itself out of recovery mode and now it is just a black screen that says iPad Unavailable for 1 hour. It doesn't do anything after an hour just keeps restarting the timer to 1 hour. I had the charging port replaced because I thought that was the issue in the first places, because the computer doesn't even show a device is plugged in. The place that put a new port in also tried resetting it with no luck. What can I do?