BT internet service and talk-talk

Hi,

we have had no problem with a btinternet broadband service for several
years. We've just changed over to talk-talk for mobile reasons, but
have stayed with the btinternet broadband. But now the btinternet comes
up and goes down several times an hour.

Nothing else has changed in the configuration - neither software nor
hardware.

Suggestions from btinternet are no help; there is no reported line
fault. We have now tried a new modem/cables etc and locking onto a bt
master box; again, anyway we try, it all suffers the same 'drop out'
problem.

Does anyone have any idea if there is any inherent incompatibility
talk-talk and BT? or are we missing something?

thanks for the help
Richard