After 12 years on Citalopram I think it has stopped working for me as well and I have relapsed with bad anxiety and depression.
I did stop and restart twice in those 12 yrs and felt dreadful when restarting but it eventually worked I've had my issues over the years but I feel back at square one with this latest occurrence and getting 5 min phone calls from an impatient GP doesn't really help to change things.
I am feeling better though and I hope you do too.🙂