I highly recommend Area 13.  They carry a 35 amp controller for Rads.  Not sure about their current stock.

Sometimes you will find the RAD 25 amp controllers on ebay. 

I have a RR5 and can't imagine keeping the 25 amp controller and the stock motor.  I also upgraded my motor.

I have 5500 miles on my RR5 bike with the original battery.  I have lots of hills and I use the throttle often.  I get the most of the mileage out of the first bar - about 10 to 12 miles.  The second bar doesn't last long maybe 4 to 5 miles.  If it gets to the 3 bar, I know I will not have enough power to get home.  So my trips are limited to less than 17 miles.

Also note that I upgraded my controller to a 35 amp and motor to a true 750 watt.  So that extra power drains me faster but I would hate my bike if I left it at original puny setup. 

Sorry you are having that problem.  I don't blame you for going to your credit card company.  Although WIRED bikes are back ordered until August, I suggest you look at their more powerful bikes for the same price.  You might not be able to import them because they are so powerful. 
Another you might consider is the Aventon Aventure 2 - same price but better specs to Rad.

I just tried to use the coupon WITHOUT luck for a rack and basket.  say not valid

looks much better than stock colors.

you might have recourse with your credit card company.  can't hurt to try.

contact the place where you purchased it from.  that's what I did when I upgraded.  but I don't have the same model or motor as you.

at first i thought maybe battery but you have eliminated that. 

have you run the bike with the brakes sensors off?  it might be a the brake lever itself that is bad.  it might just be one side. so disconnect them both at the same time.  ran the bike and see if the problem continues.  then connect one at a time test then connect the other one.   removing the sensors still allows you to brake.  the sensors tell the controller to stop power to the motor. 

have you looked at the pedal magnets to see if they are still intact?  i doubt it is this since throttle is the problem too. 

if it isn't these then maybe the wiring harness has somehow gone bad.  not sure how it could go bad just sitting there unless you have dropped the bike. 

Read your Rad manual on battery storage and performance.  The RadRover 5 I have says to not store the battery fully charged but only half charged. The newer battery versions may not have same storage requirements as mine.

Good luck

Sorry you are having the problem.  Seems like many are having the same issue.

if you want to go to the expense, yes there are upgraded controllers out. 

Try Bolton Bikes.  They might help you troubleshoot your problem and sell you want you need. They have been helpful with me in the past.

Good Luck

contact your credit card company to see if you have recourse.  my credit card company gives me lots of options for problems like this.  mine even doubles my warranty period. 

sell it and buy a WIRED.  Best bang for the buck.  I am waiting until I need a new battery to make the switch.
Rad was a good start but I was ready for more power the first day.  Ordered controller and motor.  Happy but still want more.  over 5000 miles now. 

Try Area 13.  They may have what you are looking for.  They are very helpful and respond quickly. 

Hope you are able to sell these bikes quickly.  Try listing on Facebook Marketplace.  Most people trust buying from there.  Craigslist has been good for me on some things too. 

I have a RAD Rover.  The front one is the same as the rear.  If you take that to a machine shop, they will better understand what you need.