I will bet that the solution you found is similar to this.
In the Ring 9 position of CO line programming input Dept 280. Go to Dept 280 and add members being the same as the extensions you had ringing in Rings 1, 3 & 5 of CO line programming and select the CFWD of Dept 280 to be Dept 281. Go to Dept 281 programming and add the same extensions as members there but, define the CFWD of Dept 281 to be Dept 280.
The end result will be an incoming call will ring the defined extensions 9 times then continually ring the same extensions by auto transferring in a loop of the 2 departments being 280 & 281.
Yes, this is rather clumsy but there is a reason. A phone system is engineered with the intent of being answered, that is what they do. Programming it to not do it's job requires some trickery.