If you look through SingTel FAQ, you'll find this.
However, don't waste your time calling their Hotline.
There is no phone option for termination in the first place. You will instead be put through their phone options maze where you'll probably get hold of the customer service in the end. If not, try your luck by calling again. And after wasting your time asking for details, the CSO will transfer you to instead to the termination department.
You will be serviced by another CSO who will try to persuade you to not terminate their service. They practically hard sell not just to get you to keep your Mio TV service, but everything under the red umbrella.
The best part is when in the end they will tell you that the actual termination will only take place when you return their set top box to one of the four SingPost branch. In other words, you do not need to waste your time calling their Hotline.
I do not know who came out with this brilliant idea to piss customers off because it works very well indeed.
Anyway the four SingPost branch, correct at the time I posted this, are
1.
Paya Lebar2.
Killiney Road3.
Woodlands4.
Jurong PointUpdate: As mentioned in one of the comments, it is advisable to make a
call to the branch first to check if they are able to process your termination request. Also, the items to return are the mio box, the power supply and the remote controller. Do make sure that your contract is over, else there will be termination fee. To find out if you are still under contract, call 1688.
Update: As mentioned by garfeel, you can also have it sent to SingTel Shop at Bugis and AMK
Update: SingTel customer service did say that certain Hello Shop are able to provide termination service. I guess it is best to call the outlet you plan to go first.