Hello. I recently switched from TS2 to TS3 because of the Steam sale, and I think I may have messed up few things.
First, I tried building a house for the first time after installing Uni- I couldn't move my Sims to an empty lot an I didn't know you have to build a house first, so I thought it was a bug and changed lot zoning to apartment- the translation is a little bit weird so I didn't know it was apartment type, I noticed the icon changed to a block of flats but I could move my Sims in, so I went with it.
Second, I tried to cheat my Sim to have higher education- I thought Overwatch works like Insim in TS2 and I changed values in student status (yeah, I didn't know it was available as live points reward) and my Sim had a student status while being in a main hood. I reset sim, household, tried many things etc, and finally I managed to get him back to his normal career. It looks like he still seems to have some uni-related options, but they might be some options like College Cheer in TS2 - he somehow has his higher education in bio. Like I said, the translation is really bad (mac & cheese was translated to "hamburger with cheese" for example) so I'm not sure.
Anyway, I am swarmed by roommates that I need to call off every day. I tried moving out to a true residential lot- doesn't help. Plus, the roommates problem appears in all families in this neighborhood I tried to play on. All of them. In one, there's even six goddamn roommates, so many that I needed to trap them in a basement suite so I don't die of frustration.
I googled the issue, and they say I need to call off the roommate service- but I don't have such option. I only have option to buy a lot, check lots and move out, but no roommate service.
It's not that bad that I would nuke the neighborhood or remove people and install them again, losing their relationships etc, but it's annoying.
Anyone has any idea what I can do?

You can cancel the roommate service on the land line phone,not on the cell phone. And don't forget to dismiss your roommates!

Hello ladynevermind and welcome to S3. I have a few suggestions for you. Keep in mind S3 and it's mods do not work the same as S2.

I suspect you were in UNI when you tried to move your sim to an empty lot, correct? Not sure about housing in UNI as I only play Hometown Uni's but when in your Home Town you should be able to move a sim into an empty lot that is categorized at Regular Lot.

To Cheat for a higher education: You can assign a Career using Master Controller. See See Tips For Manipulating Degrees and Academic Careers

Re Roommates: To stop Roommates from being added you need to disable Roommate Services using the phone: Click on a Sim in the Household>Phone>Real Estate & Travel Services>Roommate Services>Enable/Disable. You can see more detail for mods required and instructions by scrolling down to Roommates On This Page. Note the information under: Help, The Roommate Service Is Not On My Phone!

There are many great mods available here and on other sites. I live at NRaas and where you are just starting with Sims 3 some of these links, should you want to use NRaas, might help you:

See Getting Started With NRaas Mods I strongly suggest adding Overwatch and Error Trap as they will clean up your game and report errors.

The Gameplay Tips Page has tips, trouble shooting help and links for NRaas and other mods from various sites to enhance your play style.

The Tips For Better Game Performance has links, Tools and Suggestions to keep your game healthy along with descriptions for critical mods such as Error Trap and Overwatch.

Hope this helps you out a little

Hello! I'm so sorry for a late answer, I wrote a long answer before but forgot to click "Post".

Thank you for a long, nice answer. It was very helpful. And yes, I need to get used to TS3 being a lot different
I can write how I finally fixed the issue, so if anyone else has this problem in the future, maybe they can find this post.
Unfortunately, landline had the same options as a smartphone. And I wasn't in uni, I was in a main hood, but the lot was set as Apartment.

With some families, the mod barbarat gave me worked, the option on phone showed up. For some lots, I found out they were still seen as apartment lots, so I needed to evict my sims (btw, I learned you have to put Firefighter's alarm and car to family inventory before the rezoning, and I learned that the hard way), rezone, and move them in again. That let the option to turn off roommate service show and now I'm free from the plague :D