RF2's were traditionally used if you live in an area nearby a large radio transmitter. Their aim is to filter out frequencies not normally used by the (voice) telephone.
Unfortunately RF2's also filter out some of the higher frequencies in use by adsl and attenuate the line either to the point where adsl doesnt work at all, or vastly reducing the potential speed.
RF2's are often called "adsl killers". Ezzer will know more about this, but I believe that at one point several years ago, BT were undertaking to replace RF2's with RF3s, but obviously theres still some that have slipped through the net.
If you have an RF2 on your adsl line, BT Openreach will replace this free of charge for an RF3 (which allow the adsl frequencies to pass through). To get it replaced, you have to go via your ISP, who need to put a request in to BTw for removal as an adsl in compatible product on the line.
Its no good approaching BT (or your telcom provider) direct, since RF2's dont cause a problem with voice - only adsl hence why the request must go via your ISP.
Unfortunately you may hit a stumbling block as ISPs arent always aware of RF2's and the impact they can have on adsl so you may have to stand firm.
Funny enough both HP + myself were involved in a case within the past week or so, where someone else found themselves in a similar situation to you and was having problems getting the ISP to get BT to remove it.
In the end the ISP did put in a request and it was removed FoC by Openreach this week, gaining him a large improvement on his attenuation and sync speed.