If it is a blank income certificate, you don't have to worry, because a standard document must have not only a seal, but also the signature of the responsible person. Without a signature, a certificate with only a seal is not fully legally effective.

Now, you can ask the sales office to issue a certificate for you and reissue it at CCB.

Proof

This is to prove that my sales office of XXXX accidentally lost the income certificate of Comrade XXX. Please reissue it!

this is to certify that

XXXXX

is.