Not sure if this will really help you, but in addition to speaking with the GM, I would have advised speaking to payroll as well to discuss SL/AL hours and the payment during your time off (with the GM acknowledging rollover and the okay to pay pro-rata). If payroll was unaware of the discussion you had with the GM, they have done what they were required to do. Sucks I know, and it would have been nice of them to contact you and let you know you were out of hours and to discuss options. When I was in payroll, we had an agreement with the permanents that any SL taken in excess of entitlement + pro-rata would be taken from their AL hours.
As for the return to work plan, was the injury work related? If so, then it is a requirement they do this under Workers Comp. If not, then they were probably doing it as a 'safe guard' to ensure you weren't at risk of relapse, or the quality of your work affected if you couldn't do certain tasks.

Have a chat to the GM and see if the shortfall can be made up, and mention that you aren't happy you had to wait a further two days to return to work because of their error. I'm not sure if you will get any compensation for it, but they might make it up with your SL pay adjustment.

Hope that makes sense, and I hope it helps a little