Put one of the following commands in your "Extra settings" box for the modem. To do that, go to control panel/modems/Properties/Connection/Advanced/Extra Settings.
First, I would put "*MM15" (no quotes) in the Extra Settings box. That disables Kflex, so it shouldn't try to connect with Kflex as it may be now. Then, if that doesn't help, add one of these other commands listed below:
Start with "%B29" first (no quotes), and work your way back through the list. These limit the connect speed of the modem.
%B19 v.90/32k
%B37 v.90/33.333k
%B38 v.90/34.666k
%B21 v.90/36k
%B39 v.90/37.333k
%B40 v.90/38.666k
%B23 v.90/40k
%B41 v.90/41.333k
%B42 v.90/42.666k
%B25 v.90/44k
%B43 v.90/45.333k
%B44 v.90/46.666k
%B27 v.90/48k
%B45 v.90/49.333k
%B46 v.90/50.666k
%B29 v.90/52k