Is there no guarantee of Limit Orders execution?

Last Friday I've noticed a strange TP execution of my order. It was closed with huge negative slippage of 37 points (3.7 pips).
As far as I know TP orders are to be executed as Limit orders which means that at exact or better price. So we may expect from zero to some positive slippage. I considered it as a server mistake and applied to my broker support to explain or resolve it.

And I was greatly surprised to read such an answer today:
What does it mean? Have I missed something? Is it only IC Markets who is executing Limit orders as Market orders? Or is it already no execution difference between Stop, Limit and Market orders at all?

First there is no Limit Orders in MT4, you only consume liquidity you cant supply liquidity. To do that you need a real ecn broker and a real FIX platform that they provide you like dukascopy which has jforex. In MT4 your limit or stop are being hold in the server and if price at a point reach the exact price of your limit order then its being execute as a market order. IC markets i think they support ctrader , it has more cost than MT4 but there your limit order is treated like a real limit, so you can try it. About slippage Customer service told you , your orders are being filled in the best price at the moment and also at that moment maybe the liquidity is low and market is gaping and spread is widening.

P.S. sorry for bad english

Thanks for my markets knowledge increasing buddy.
It seemed that broker is ECN.

So we have to be aware of Limit Orders absence on MT4.
Bad news ...

YES IC Markets is an ECN like broker. But remember only the orders that are above one lot are heading straight to be matched in the market or the other ecn pools outside of your brokers liquidity pool. Less than one lot your order is being filled by the broker or any other client he has or its partners in the ecn pool are having.
MT4 and ECN doesnt go hand to hand.

There is no guaranteed Limit , Stop , TP or SL trading with a ECN Broker and all orders are executed as market orders. These are settings you make on your MT4 Plattform at specific price. Once this price gets triggered the order will be sent for execution to the market, thus you can have negative or positive slippage like your broker said. Some market makers used to have these options for guaranteed stops and limits as the orders never get to the market and are staying inside the brokers house but that is another story. With ECN and market orders you have to accept slippage negative or positive is pretty normal. Cheers