Well, I can tell you from my experience what I did when I forgot the number to my new telephone line. The easiest of the solutions which I could think at that time was to call on my cell number from the new telephone. And because of the Caller Identification feature I was able to see my number and then saved the number in my mobile.
You can do the same, if you do not have the cell phone then call on anyone of your friends or family members and ask them to tell you the number from which they received the call. That's the easiest way to solve this problem in my opinion. Caller Identification is a very common service and it is readily available through all the Telephone Service providers for local and international calls.
Also if you do not want to choose this option then I would suggest you contact the Telephone Company. It won't be a hassle to them because they receive different types of complains and the problem you are facing is not a unique one to them so I would say that try the suggestion that I gave you. It will help you out.
You can do the same, if you do not have the cell phone then call on anyone of your friends or family members and ask them to tell you the number from which they received the call. That's the easiest way to solve this problem in my opinion. Caller Identification is a very common service and it is readily available through all the Telephone Service providers for local and international calls.
Also if you do not want to choose this option then I would suggest you contact the Telephone Company. It won't be a hassle to them because they receive different types of complains and the problem you are facing is not a unique one to them so I would say that try the suggestion that I gave you. It will help you out.