How can this happen

I apologize if this is wrong area but it is security related.
I can't make or receive landline calls at the moment yet on Saturday my phone rang, it was the well known, bla bla bla we have noticed suspicious activity on you internet press 1, I hung up.
My landline was with Talktalk, is this a breach of security with TT.
Anyone any idea how this can happen.

When you say you can't make or receive calls, do you regard that as a fault, or by choice, or is that a restriction the account holder requested be in place?

Otherwise the general case for landlines and telephones is that no-one needs permission or authorisation, or even foreknowledge of who you are to call your number, just like no-one needs permission or authorisation to put something in the post with your address.

Therefore it would not normally be a security breach.

As regards autodiallers, there are acts covering conditions for when that activity may be unlawful but even then is considered the fault of the organisation making the calls rather than which telephony provider you happen to have your phone number with.

If you don't speak first, many autodiallers will hang up before starting playback, because they are waiting to see if they get a voice, a fax tone or other signal (engaged, out of service, unobtainable). Official advice is that a genuine caller will still speak first, even if slightly surprised by silence when picking up.

As regards any unwanted call yes you can just hang up or put the phone down for a few minutes before returning later to hang up.

For the "suspicious activity on your internet" you can play with them if you wish.
My current favourite is to ask:

"… oh that is indeed concerning. Please tell me which computer is causing the problem?"
> "erm … (confused noises)?"
"Yes - can you tell me the hostname so we can check on the one affected?"
> "(muffled chatter)"

I don't know how to use quote on this forum, I have posted under Talktalk, I am moving to Plusnet and TT have not released the line or whatever terminology is used, my changeover date was 14th July, my phone/BB went of at 09:30 on that date.
Plusnet could not complete the move because of TT, note I did not terminate the TT account, I left the process to Plusnet who incidentally have been very helpful.
I wouldn't normally answer unknown calls but being in a state of flux I thought there had been some progress, silly me.
I wouldn't dream of encouraging them just keep adding them to the blacklist

This why I'm curious as to how a phone call can be made under such circumstances.

If you dial 17070 you may get told the number of the line which you can then ring from another phone.

If 17070 doesn't give you the current landline number then you can try 02087599036 instead.

17070 doesn't work on Talktalk lines (or any LLU phone number).
02087599036 is basically 17070 for non BT Wholesale lines.