First, you need to collect info about your connection before 'investing' in another modem/router. More often than not, it is due to poor line conditions that one has to face disconnections! You can find the line stats and post them here though it may be noted that line conditions vary over time due to noise and line stats at one point in time shall not give us the full picture. If it's the line at fault, then another (better) modem might help only a little or even not at all!
Most recommended way is to look for alternative (internet) connection as it's quite difficult to have the problem fixed unless you are lucky to get a good pair (that may also fail at any time) ... the support staff don't even carry professional equipment such as a line tester and just go about on their whims ... I would go as far as to say they don't even know how to splice wires!
We are also in the process of closing our connection due to such problems and moving on to something better (even if it means to sacrifice 'good' bandwidth cap offered... if we can't use it properly then what's the point of 300GB) ... and yes it is quite a process to shut everything down, but, I can already taste the freedom!
If you want to push your luck or you get lucky, you may get any router/modem/gateway that supports adsl2+ with good reviews online (Netgear and ASUS have some good new dsl ones but availability might be limited here) ... just need to configure it for PTCL (Fiber or Copper VPI/VCI, PPPoE with LLC, username and password for dsl) ... I have a selection of few routers for sale here and here I am collecting info about using the ones for UK ISPs (these are available here locally) as well!
Hope this helps!