From your timeline, I see you applied in October and got your PCC in december. PCC validity is measured against when your application was submitted and it is clear that since you got in December, your pcc is no more than 2 months from your application date, you should be fine.
Here's what I suggest. Send an email to Ottawa (since you got the email from Ottawa), stating that you've sent the PCC, attach proof of receipt at CIC.
On a side note, it looks like you sent the PCC before CIC asked. It is always good with immigration to follow instructions no matter how anxious you are - this way, if something goes wrong, you can show that you did all that was asked of you. Did you send the PCC to Sydney ? I see now that Ottawa is asking for it as it appears your file is actually in Ottawa. That's why it's always good to just wait for the correspondence that tells you the address to send it to. Overall, I think an email should solve your issue.
