For those still having error 837, I recently had the problem and solved it.
I was trying to activate with the device IMEI to port my number over. Instead, I used my old account number from previous provider (Telus). You can port your number using either IMEI or old provider account number; I was wary of using my old provider account number because there was two phone numbers associated with the old provider and I was worried it would interfere with the other - it didn't, I ended up successfully porting both numbers using the old provider's account number successfully (one single account number used twice, once for each new Public Mobile account).
So to me it seems most likely that error 837 occurs only when trying to port phone number using IMEI. Try using old provider's account number instead.
Before I figured out this solution, I did also talk to a chat agent and they suggested creating an account with a new number and then attempting to port the number (i.e. create a new Public Mobile phone number when activating, then immediately do an old number port in self-serve). This might be a good solution for you if my other solution doesn't work.
Hope this helps. 👍
