Actually not true. If your telephone wires is located on the ceiling board, the heat and some moisture will cause the wires to degrade. If your wires are very old ie >5 years, and you have poor SNR, it's worth looking to replace those wires. Or pull a separate wire

My sympatheties on your line attention. I also same same.

To answer your question, once Telekom wire enter your house (where they clip their cable to yours), anything after that and in your house, is your responsibility. That is what you call internal wiring. So yes, have to pay.

But RM100 seems pricey. You can try to get a wireman to do it. It will depend on length of cable and if you want casing or concealed.

Actually your SNR doesn't look that bad as mine. At least >10db. When you say frequent disconnect, you mean at specific times of day? Did you check the DSL parameters when that happens?