I have to agree that this thread is getting out of hand. My mind was blown when I first read it a couple days ago and it is only getting worse. I understand you want to help your landlord out, but you do not have the knowledge to do so on a technical level and the information you are finding online is either inaccurate or hurtful to your burgeoning "network specialist career" that you seem to be chasing. Not everyone has this knowledge and that is fine, but you are ignoring the people that do have good advice and latching on to random sentaces that you shouldn't be. On top of the fact that this is not even a technical problem and does not require a technical solution.
What hasn't been stated so far is whether internet service was listed in the rental agreement as a service to be provided as part of the rent as was signed by both parties. If it wasn't, then the landlord can cut the tenant off with no concern. If it was, the Residential Tenancies Act of 2006 has this to say about cutting off the tenant's service:
Reduction in services
130. (1) A tenant of a rental unit may apply to the Board for an order for a reduction of the rent charged for the rental unit due to a reduction or discontinuance in services or facilities provided in respect of the rental unit or the residential complex. 2006, c. 17, s. 130 (1).
...(section 2 applies to former tenants)...
Order re lawful rent
(3) The Board shall make findings in accordance with the prescribed rules and may order,
(a) that the rent charged be reduced by a specified amount;
(b) that there be a rebate to the tenant of any rent found to have been unlawfully collected by the landlord;
(c) that the rent charged be reduced by a specified amount for a specified period if there has been a temporary reduction in a service. 2006, c. 17, s. 130 (3).
(4) An order under this section reducing rent takes effect on the day that the discontinuance or reduction first occurred. 2006, c. 17, s. 130 (4).
Same, time limitation
(5) No application may be made under this section more than one year after a reduction or discontinuance in a service or facility. 2006, c. 17, s. 130 (5).
I'm not a lawyer, but having just read through the act; this seems to be the section that best applies. Have the landlord contact a lawyer before acting and offer the option to decrease the rent up front so that the board does not need to get involved. In any case, this really is the final option. Attempting to use technical measures that you really do not know how to use is not a good option, ever. If your landlord is concerned about souring the relationship with the tenant by approaching them for my 2nd best or final options, (s)he shouldn't be; the tenant has already accomplished this by not acting appropriately when approached the first time.
Re-reading the thread, you state internet service was not listed in the agreement. "Possibly might be" is not a promise, nor would it have been included if the landlord had had the agreement checked by a lawyer (always have it checked by a lawyer!). Cut the tenant off as a last measure and don't worry about it as long as it wasn't added to the agreement after the fact.