I've just moved house and have a new internet setup, Zen Internet, the ISP has supplied a FRITZ!Box 7530, and I've not been able to get remote access to the DVR working. Digging around I've come across this which explains that FRITZ!Box use port 8089 for router TR-069, and there is no way to switch it off due to the way the ISP have configured the router - the option described in the above link has been removed.
Is there any way to switch Remote DVR to some other port?
Create a port forward rule that uses a different external port to forward 8089. When you authorize your remote device you will need to right click on the authorize button and copy/paste the link, modify 8089 in the url to the manual number you assigned and then click enter.
I wish there was an easier way to do this, similar to how plex has a setting to inform it that you are using a different external port, but until a cleaner solution is added this is your best option.