Obviously it is not. What equipment are you using?
You can complain to TM via 100.

When you run the Speedtest, did you use LAN cable or WiFi?

And which router is that?

This one can't do any magic. Call TM to replace new router for you, saying the current one is not capable to achieve 50Mbps.
Or you buy a new router yourself.

Get TM to replace the router, The TP Link AC1200 or D Link Dir850L shud be able to support 50 mbp.

Where are you going to use it? At home or at the office?
If at home, how many devices will be connected at 1 time?

If not more than 20 devices, just get the ASUS RT-AC88U. It's more than enough
The RT-AC5300 is over the top for home users. And most homes won't even utilize the tri-band on RT-AC5300. Dual-band on RT-AC88U should suffice

But if you still insist on getting the RT-AC5300, it is still a very good choice. It's a monster really

which model router that tm gave you?
may i know why you say not so good?

thanks,,,

I thought they give c5 not c7?