Is my landline hacked or it was call from telecom?

Yes, they were working on your line. If you are confident of the identity of the other party's voice, the problem is most likely in your neighborhood. Testing, repairing, and proving a phone line will sound exactly like what you describe. As far as them hearing any part of your private call, it is also likely and part of the repair process, to be familiar with the symptoms and then knowing if progress was made. After replacing parts and adjusting the wires techs must listen, just like you do. Don't stress over it, they have heard it all already many times over. It is so normal, they don't even talk about it anymore. Nothing they hear is allowed as evidence either.