Having major issues with internet or ISP itself

Possibly the best thing to do is to call them up and get the fault number so you can keep pushing them on it and keep track of it. imo ,if your paying for 100~160 you should not be paying it if your not getting it. id check about compensation if they are taking their time to send someone out and your going a month or more with a degraded line. (their minimum is 40 at half the price of 160, and your not even getting that)

Bad lines can cause these kind of issues if they were poorly installed or damaged. The fact that you were getting 100 originally on what appears should be a 160 fibre line might mean there’s always been a problem.

Have a look here for some information on what you can do https://www.ofcom.org.uk/phones-telecoms-and-internet/advice-for-consumers/advice/broadband-speeds-codes-practice

If the issue is in their network and they can fix it you have the right to exit without penalty, however the rules don’t specify an acceptable resolution time yet (new rules change this but they are not in yet). But that doesn’t stop you from pushing them, asking for a discount or shaming them yourself until they give you what you want (assuming the issue is there’s to fix).

On the ISP side there isnt a lot you can do depending on the ISP.

On your side, Ethernet is better than wifi especially in densely populated areas. You may find changing DNS from your ISP to another provider (8.8.8.8, 1.1.1.1 etc) will be faster, how fast depends on how good or bad the ISP one is.

If you have a lot of devices you might be able to prioritise some depending on time of day etc if you need to within your router.

Additional information: If the lines are degraded and in need of replacement, that means the signal that the lines carry are leaking said signal to such extent that your download/upload speeds have degraded to the same extent as the lines themselves due to the insulation of that/those same line[s] being in a degradation state.

Update.
Im fukcing pissed because I just started school and im resulting to using my phone’s hotspot for reliable internet. Yes, my mobile data is more reliable than my home HARDWIRED internet.

Internet has gotten worse. I cant even stream 160p on twitch or even play games that are online based. Im looking at 5mbp/s when we pay over 100 dollars a month for 100 mbp/s. They’ve sent techs out 4 times with zero changes in reliability. They say that they’ve repaired some lines outside but like I said, it’s just gotten worse. On top of that I cant access the router to see whats up bc they wont provide me or my sister with the login details (even thought we’re both on the account). We’ve both come to the conclusion that wither we’re getting throttled as expected, or our router is complete ass. This would not surprise me, as its some garbage brand I’ve never heard of (sagecom). Any suggestions would be nice.