HDFC Bank — Frequency ADHO was rejected

Address: CHILAKALURIPET

I have taken loan in YesBank. For that I did signature on the form for enabling the auto debut on every month. But I got the below message.
"Dear Customer Mandate reference no: HDFC[protected] issued to YES BANK RETAIL ASSET with value Rs.26239 and frequency ADHO was rejected due to the reason 'Drawers Signature Differs' received today for processing."
I dont why it is getting rejected. I have applied for twice. Twice it was rejected. But the signature is correct and I withdrawn the money also with same signature. So please accept this ADHO reference number.