I understand that TiVO have an 'easier' warranty repair/replacement policy (similar to Apple) but in this instance the customer did not know this so made the trip to the retailer. This fact alone should have warranted better after sales service then OP received. Had the customer called the store first and enquired about the process then the retailer would be fine in encouraging the phone support.
In hindsight, what the store should have done in the first place is provide the customer with a warranty card explaining the process for dealing with faults; this is what I do for all customers purchasing laptops and other expensive gear from me.
The problem I have with this situation is the attitude of a retailer when a customer returns faulty goods. This situation is never a good one for a retailer but they always have the option to have the customer leave feeling satisfied and remain happy with their purchase. Fobbing a customer off to move on to the next paying customer may help your bottom line in the long run but will generate a reputation you will not like in the long run.
This thread hasn't been a Telecom bashing one either. I do not think Telecom NZ Ltd. is at fault in this situation nor do I think they are totally blameless. If you franchise your brand out to another company it is your responsibility to make sure your customers are being treated correctly. As the OP has shown, your customers will not always know that Telecom retail stores are not run by Telecom.