As davidmak said, there is normally a clause saying all terms and conditions are subject to change without prior notice. When you sign the contract, you accept that clause / term. You are then bound by the new terms and conditions when it is revised.

To a point, it is technically valid that TM cannot guarantee access outside their control. Data traffic flows through various connections, routers, servers etc in various locations, countries etc under the control of others. Any fault elsewhere which affects the data traffic cannot be directly rectified by them. This is the same for any ISP. The Internet is a coloborative network.

However, while TM has the right to insert the new clause, a responsible company who has nothing to hide would at least inform their customers about it.

Can you say where to?