Extremely disappointed customer

So my husband and I got ******,and today I phoned cellc customer care to block the cell numbers because it's being utilised by someone else.. and come to the security part and the consultant tells me I need to know the last 3 numbers I have dailed... How am I supposed to know that.. I deal with so many people on a daily basis how would I remember those number without my phone.. and when I try to explain my situation the consultant then says I have already failed the security questionaire and can not be assisted any further..I have been a loyal customer for almost 10 years with cellc and this is the treatment and service I get.. absolutely disgusted and heartbroken.