You need to report it to TalkTalk who will then warn you that if the fault is inside your house you could be charged for an engineer's visit. You seem to have proved to yourself that the fault isn't yours by plugging a corded phone into the main socket (I assume the cordless base was not plugged in anywhere), so don't worry about that. A final check to make is to call your landline from your cellphone - the result will be interesting to Talktalk. Talktalk will probably offer to divert incoming calls to your cellphone, if you have one, at no cost to you. On the couple of occasions we've had line faults Talktalk have been very good at keeping us up-to-date via texts.
If you internet is still working (how else would you be posting on here?) you can report the fault by logging in to your account.