... I deliberately waited a day before giving my two cents here.
First of all: Under no circumstances am I trying to make Telekom look bad here!
I have been assisting mainly business customers with the creation of internet connections for well over 20 years. Mostly Telekom customers, but of course in recent years increasingly also Unitymedia/Vodafone, Deutsche Glasfaser, 1und1, Versatel, etc.
A book would not be thick enough to recount all the "stories" that have happened along the way. On this I can swear under oath: Not a single! order went from start to finish exactly as the customer wanted or commissioned. Mostly there were only (small) delays and other minor issues that were quickly corrected or similar.
Sometimes though really "big blunders" like totally wrong orders (so other things were done than what the customer ordered), massive delays for large customers of more than 3 months (the connection then came 3 months after moving into the new company building, caused by the mid-market sales department (wrong order) combined with extremely poor communication. The left hand doesn’t know what the right hand is doing.
(Temporary) loss of phone numbers or availability due to unannounced/unplanned activations, etc.
In my opinion, friendliness and service have improved in recent years! And that applies to all companies. Even if calling the hotline is still not a pleasure, because nonsensical / nerve-wracking voice menus are simply no fun!
Now here comes the kicker: Despite everything, I expressly recommend Telekom as a contracting partner (especially in the area of telephony), because: The other providers on the market are not better. Only where Telekom cannot deliver (at least 100 MBit/s) does UM/Vodafone (sometimes only as an addition) come into play.
I have experienced that individual employees care and take customers seriously at all providers. That should not be concealed as that does happen. Overall, there is still much room for improvement in the telecommunications market.
However, since current laws in this area are rather broadband expansion prevention measures as the lobby of the quasi-oligopolists has taken appropriate influence, I do not expect any improvement here in the short term. As already said: This belongs in public hands (just like electricity, water, and roads)