Citibank Debt Collection Complaint

Citibank Debt collection department,

I do not know Communication tactics Frequent or repeated calls California

- - - , - repeatedly call me on my cell phone, which is my work phone. When I say Hello, hello, no one is there!!! I repeatedly asked them to Validate this debt, which mentions - and as I see from my credit report is quite old, but they keep sending me a letter saying they are requesting the appropriate documents. The last time they called, I took a photo of the call on my cell number. - removed their entry from my credit report but - is not willing to do so.