800-634-7099

D... wrote:

...because they called me twice on a Saturday morning.

Hardly a good test for legitimacy of a call from a debt collector (and the previous posts indicate this is either a debt collector or some one posing as one).
On the Government of Canada website on the page "Dealing with a debt collector" the days and times a legitimate debt collector can call are listed:

Government of Canada wrote:

When a debt collector can contact you
A debt collector can only contact you at the following times:
   Monday through Saturday between 7:00 a.m. and 9:00 p.m.
   Sundays between 1:00 p.m. and 5:00 p.m.
A debt collector can't contact you on holidays.

D... wrote:

I do not have any cards or accounts related to Home Depot!

Now, that is a far better indicator that the call may be a scam than what day of the week they called.
But, there is the chance that it is a legitimate call from CITI for a card holder that had your number prior to it being assigned to you.  I guess you will never know for sure, since you will not answer the phone.

When I pick up there is just silence. No ones ever there. This number call 4times a day! It’s so annoying! 😡