1. If you know the addresses of these houses get the title deeds for all of them from the Land Registry (make sure you use the gov.uk site - others do the same thing but are run by people who charge much more to do it). Then you will know whether you are in fact named as part owner of any or all of them.
2. If you are, then ring the land registry helpline - they will tell you whether it is possible for you to have been put down as part owner without you agreeing or signing anything. I'm pretty sure it can't be done, but it is as well to get it confirmed. Ask them whether they can send you a copy of the documents bearing your signature so you can check whether it bears any relationship to your actual signature.
3. If you are down as part owner & are absolutely certain you did not sign anything, then your mother (or someone else) forged your signature. That is fraud & a criminal offence. You then need to decide where you want to go with that.
4. If you want, you can skip all the ad just do what PP suggests. However, as you obviously know, if the local authority finds out (even after your name has been removed) they can create a (possibly very large) housing benefit overpayment & even try to prosecute you for fraud. So my view is you should go through steps 1 - 3 above & then take some action to get it put beyond doubt that you did not know about this before & that forgery occurred.