Why was the position not closed even when the price was on the chart?

Remember that there are two prices in the market: the price of sellers (ask) and the price of buyers (bid).

The chart shows the bid price.
So:
  • A sell order is opened at the bid price, and is closed at the ask price.
  • A buy order is opened at the ask price, and is closed at the bid price.
Consider this example:
 
For your SELL order, the stop-loss order is set at the price of 1.2970. The price in the chart reached 1.2968, but the order was closed by stop-loss price. In this case, 1.2968 is the bid price, and given the spread of 2 points, the ask price was 1.2970 (i.e. ask = bid + spread = 1.2968 +0.0002 = 1.2970).
 
SELL orders are executed at the ask price. Therefore, the SELL order was closed by stop-loss order at the price “bid 1.2968 ask 1.2970.”