It seems like their servers are down or something, me and another person have the same issue

Check self serve now. It may be up and running again 

Got the same offer and keep getting this error message. Has anyone had any success? Tried on my phone device as well as a desktop 

 To Koodo. 

 I received the same text message from Koodo the other day about an exclusive offer. I logged into Self Serve and the offer wasn’t there. How do I redeem this offer? Can you please provide an update. Thanks Larry

Self serve>mobile services>change my plan

There you will see your current plan, exclusive offer n regular plans.

Choose the one you want and proceed 

@Bugsy Most of the people here who posted were seem to have been able to change there plan after all.  Pls follow @Jenny Duong suggestion, if you run into issues let us know here.