Sathya Agencies pvt ltdcoimbatore - Billing Discrepancy and NonRefund of Excess Payment

I am writing to formally raise a concern regarding the purchase of an HP laptop on **/**/**** from Sathya Agencies pvt ltd store located at No: ***, ***, Rajendra Prasad Road, Gandhipuram, ***ft Road, Coimbatore.
The payment was made as follows:
₹*,*** through GPay (Transaction reference available upon request)
₹**,*** through Bajaj Finance loan
Total paid: ₹**,***

However, the online invoice I received was only for ₹**,*** (Invoice #: ******CBE*******), not matching the amount I paid. Upon inquiry over phone, staff assured me that the remaining balance would be refunded within two days. As of today (**/**/****), I have not received any refund.
Today, I visited directly in shop again to resolve the matter, but I was handed a new bill for ₹**,*** (invoice #: ******CBE*******) which:
Does not match the actual product serial number: *CD****Q*Qof the HP laptop I purchased.
Raises concerns about potential misrepresentation or invoice manipulation.
I request that you:
Provide a correct bill matching the actual HP laptop I purchased, with accurate serial number and IMEI (if applicable).
Refund the excess amount if any discrepancy exists between the actual product value and the paid amount.