I think it's on DVB-T only. When did you buy the TV?

Are you able to receive all analogue channels clearly?
Have you tried changing other cables? Do make sure the cable type used to connect to your condo's centralise TV antenna port is RG-6 type, not those cheap old ones as it may degrade the signal.

How about your nearby neighbours within your condo block? Are they able to receive all digital TV channels via centralised antenna?

If still cannot, contact your building management to check on that. Or, you can contact MYTV customer service at 1800-18-1088 and tell them the issue you're facing.
MYTV might contact your condo building management to provide some solutions.

Yet, if these are too much of a hassle, get a good indoor UHF antenna, or set up your own outdoor antenna.
If your building management doesn't allow own antenna to be installed outside, try place it in a spot where it doesn't look too protruding and obvious, while able to get stable signal of 666Mhz and 698MHz.
Perhaps, no one would notice and complain, and they would just close one eye 
I dunno how strict is your condo management, so don't blame me ya...
But if later they tell you to take down the outdoor antenna, then take down lo...