HDFC NIF ETF not mirroring NIFTY on 16th and 17th March

Query

On 16th March 2020 I purchased 40 nos of HDFC NIFTY ETF ( Ref: Contract number CNT-19/20-49799895 at price of 1115 and it’s closing price was 1175. On 17-3-2020, it is opened at 1160 and dropped by about 15% subsequently . HDFCNIFETF mirrors the NIFTY 50 .Nifty is up by 135 by noon on 17th March and HDFC NIF ETF was trading almost 17%(1006 to be precise)below previous day closing price of 1175. This being the case how can HDFCNIFETF drop as much as 15% compared to previous day closing price. I request you to kindly investigate and help me .The loss to me as a result of this is approx 4360 rupees. Issue is not the loss, it’s the system reliability between HDFC AMC and NSE.I have tried unsuccessfully to get the answer from HDFC AMC. I look forward to your help.
Thanking You,
Laxmibai S Balawat.

Check this.

It is a big lesson for me. Lost close to Rs4500/-
To check NAV before buying the ETF is the lesson.