Anyone receving US Social Security benefits in Bulgaria? Need advice

I have applied for my US Social Security Retirement Benefit, having worked there for 13 years (many years ago).

Now, the Federal Benefits Unit in Athens told be to fill the form SSA-1199 BULGARIA if I want the money paid into my Bulgarian bank account. The form is in 3 parts, and the last one should be filled and stamped by the Bulgarian bank, to certify my account details. The form is entirely in English, I don' know how the bank clerks will react to my request to fill their part of it. I have accounts in two banks, Texim and Obwinska Banka (the Municipal bank).

I suspect that there are other people, whether Americans. or those who have worked in the US, who have been there. If you have, could you advise how I approach either of my banks?