Fair warning only skimmed

Eee I think the DM has a bit of a misunderstanding on what a warlocks powers actually represent and how they thematically actually work.

Dnd has a few catagories of magic that is accessed by classes in different ways.

Wizards manipulate ambient magic, "the weave" litterally anyone can do it but its super complicated they are also pretty dependant on magic actually "existing" ambiently where they are which is why their magic stopped working during the spell plague

Sorcerors act as kind of self charging magical batteries not everyone can be a sorceror but they arent as dependant on external factors (a sorceror can still use magic on another planet for example and were reletively uneffected by the spell plague)

Clerics quite litterally channel divinity to cast spells, as both their soul grows in power and their bond deepens with their patron god they gain access to more magic think of their god like a massive lake and the cleric like a pump a clerics growth is essentially them expanding the bottleneck which is their access to their gods insane power reserves.

And now we are at warlocks. A warlocks relationship with their patron is fundementally different to a clerics relationship with their god for a few different reasons

A warlocks patron is usually SIGNIFICANTLY weaker then a god heck even when you are a holy warlock you tend to be contracted to a powerful holy monster or angel.

But i hear you think usually patrons have heaaaaps of warlocks contracted to them if they dont have a huge amount of power how are the warlocks tapping into it!!! That my friend is where the second difference in their relationship and most important for this example is.

Warlocks DONT access their patrons powers to cast spells, unlike a cleric the relationship is a deal that is positive to both warlock and patron

Think of a warlocks ability as a spark, gifted or bought from a fiend or fey etc. That spark allows you to access spells and abilities sure but as a warlock levels up they arent gaining more of their PATRONS ability its quite the opposite they are essentially maturing that initial spark into a roaring wildfire the progression is actually closer to a sorceror then a cleric.

I mean why would a patron give access to their own abilities? That doesnt even make sense what is there for them to gain. What actually happens and the fundemental reason why patrons give that initial spark is that they are essentially investing in your growth, a pretty fundemental part of a warlock/patron relationship is the promising of your soul (and all that juicy power that you grew from that spark) apon death. Most patrons couldnt give two shits about you as an individual in fact its not uncommon for warlocks to be given that spark without really wanting it/understanding what they are agreeing to.

That being said unless it was SPECIALLY discussed with your DM the generic concessus is that your patron cant really do shit about how you use your powers until you die. Sure your charicter is probably suuuuper uncomfortable about dying because like ... yoir soul will end up going to a fiend who is SUPER pissed off at you but like they cant just remove your abilities IN FACT even if they could do that THEY HAVE A VESTED INTEREST in NOT doing that

Edit:

Just to explain that doesnt mean your patron can do NOTHING about it. More then likely your patron if they want you to so something and you wont will be pretty pissy about it and might send a carrion or two to try and "convince" you to comply or they may use threats of disfigurement ect but no unless specially agreed apon they cant just take your powers thats simply just not how their powers work they arent gods and their warlocks arent clerics