As i mention before. Go to the tm website. Use the email support. It'll take within a day or two for them to reply u.
I chose 4mbps because my area also no unifi.

yeap.
Though i use this to email them.It'll generate a standard format instead of us arranging the format ourself.Remember to select category as broadband. Most important to fill in is the telephone number tied to ur broadband.

actually they only need to change your port at their side

just to make sure your line is eligible to handle the 4Mbps rate so there's a technician or contractor will go there and make sure everything is working as it should

Port at their side i assume is referring to the DSLAM. Usually i think most users will provide their location/address to tmpoint customer service/helpline. Their system when entered with the provided information will usually return nothing. Maybe providing them with the service number*the tel no tied to ur streamyx* might yield a different result.
Just my guess.

Ur installer mention that it's capable of handling 4mbps means ur line is eligible for 4mbps. It's just that requires tm side to activate it only.
Their RM140 plan quite attractive. one wireless modem and one wireless dect phone free.Though i'll still put the useless modem aside lol. And unlike unifi , if landed property during thunderstorm =.="...... no streamyx for you. Unless you want the thunder to come in through your telephone line and fry off everything.