Prestige 202H/ISDN/CENTREX: breaks connection every 10 min. - anoyone had that?

I'm surely positive that:
- problem exists only on one end (the second one serves another link without
problems)
- the router is ok (I swapped it with working one and it failed)
- yes, it's probably telecomm provider problem, i've reported it, but
waiting is killing me

So that's why I'm asking if there's anyone with some experience in local
telephone station equipment (or fighting lazy, stupid and stubborn telecomm
company?
Or maybe I'm missing something?

Any hints?

Thanks.