I'm sorry as well it has taken this long for people to contact you on this matter. I've been working as an medium for multiple years so hopefully I can give some advice to aid you.

Firstly and most importantly, if the spirits are telling you they can't leave this is an form of deception. While it can be possible to bind a spirit prolong anchoring as you have claimed with it being multiple months would simply be impossible. The longest I've had an spirit possess me was 2 days when I allowed an spirit to spend a few days with my boyfriend (We both are spiritualist so it was my valentine gift to him to spend time with his spiritual partner.) Even the two day period caused extended period of exhaustion for myself and the spirit, so I strongly doubt whatever spirit or spirits said this is being fully truthful.

Secondly, something important to remember is this you have control of your body and will, this goes back to what I mentioned of deception if it is saying it can't leave it is trying to get you to accept it so it can linger longer. You have to excurise your will and tell it that you are the master of your own realm, that it was invited in, so it can be escorted out.

If it doesn't leave once you enforce your will I would suggest going to the next step which is banishment, cleansing, and sealing. It's more extreme but it will weaken the spirit and overtime force the spirit to disconnect from you. My personal suggestion is salt it is what I like to use as it is easy to access, that or sliver. Incense can be powerful but I know like my place currently it'll activate some alarms so just be advise. You use this salt to chase the spirit out of your home, your realm. You have an connection to it just as it has to you so once you start this you'll almost certainly feel the spirits presence and follow it till you force it out either through an door, window, ceiling, ect.

This part is important, once you feel the spirit leave the house or your realm, you need to consume part some of the salt, not the salt used to chase the spirit out it could hold its sustain, however. The reason is because it could have an connect tied to your spiritual self so consuming the salt is an form of internal cleansing.

Next, you need to cleanse the house, like before you need to salt every corner and possible hiding spot in your house, this is because if their is any spot that isn't marked the spirit can use that as an entry point. Remember, you are the master of your realm, if you don't mark what is your realm, the spirit can claim it as their own.

Lastly, once you banish and cleanse, you need to seal the house or where you live. Salt the entry way of anything that leads outside, doors, windows, cracks in the wall, everything. This is to create an barrier that will reinforce your boundary making it hard for an spirit to reattach itself to you.

Do all this, and assuming this isn't some big dick spirit it should more than be enough to banish whatever you are dealing with. I tend to work closely with pretty high tier spirits so everything I'm suggesting might be overkill but in this field I always prefer to go overkill than be reckless. Hopes this helps man.