I had experience with a lightning strike in the US. So, this may not be applicable to you. First, disconnect everything plugged into the system. Then, find an old fashioned phone (one that is not electronic) and plug it into your system. Do you get a dial tone? If not, go to the service entrance box and see if you get a dial tone from the incoming wire. If you are cable, go to the modem. In the US, we have access to that box. If you can't get a dial tone there, then you need to contact the service provider. If you get a dial tone, then you need to find a pair of wires that are not vaporized and/or shorted in the house wiring. If you have a helper, it makes that search much easier. Once you get t he functional pair, use them for your wiring.
You might also want to open every wall box. Some of the damage to wires in our house were just in that box and was easily fixed. You may not be able to use the original colors, but that makes no difference.
If you don't have an old fashioned phone, use an electronic phone that is known to work.
John