phone was stolen, apple pay was suspended, but then used without my authorization

Apple Pay can’t be suspended. There is no function in iCloud/Apple ID to suspend Apple Pay. The closest thing to suspending Apple Pay would be going into <Find My> and locking your iPhone. You would have also had the option to erase your iPhone.

So, did you lock your iPhone or erase it? There is no suspend Apple Pay.

Nobody can get into your phone or use Apple Pay without your Passcode. If you see charges on your bank statement and the they did not know your Passcode, then the charges did not come from your device. I would be checking into another way that your card numbers were compromised. The likelihood that someone guessed your passcode is nil, unless it was something like 1111. The device would have locked automatically.

The only way the thief could have gotten into your phone is buy knowing the passcode. If your passcode is simple it is entirely possible thief was able to guess it. Normally iOS allows ten tries before locking up.