LG Electronics — Taken extra interest charges on No emi cost

Dear Concern,
I bought an LG AC from Sahu agencies kapoorthala, lucknow at the rs 40290/- . I got brand discount of Rs 2000/-. and finally I paid rs 38290/- through ICICI credit card in 9 month EMI Rs 4506/- per month on NO EMI COST scheme. . Mr. Ashish ( sales Man) and his Manager committed to me. he will not take any interest charge to me. however I have to pay, Interest charge Rs 2264/- and it will be cash back by the bank . I informed to them that It is clearly written in sales invoice that only Rs 1500/- will be cashback. he said to me don't worry you will get all interest charges after 90 days. when I return back to him on 12 June 2022. he refused that and said no interest charges are taking from you, all are processing charges only, I have shown to him my credit card details that I am paying interest and it is not any processing fees.
Kindly help me to get my interest charges Rs 764/- ( Rs 2264/- less Rs 1500/- cash back received).