Mtnl broadband Adsl connectivity not stable

I've activated mtnl's broadband on my landline 5419 number since more than 5 yrs now. However, since past 2-3 months adsl connectivity is not stable. I have complaint mtnl numerous time but the technical official narrow down the cause to my home pc. Technical official says it's a pc issue, which is absolutely wrong. The connectivity to their dns server I.E 3.70 and 3.70 is very very un-stable, which is resulting to very slow speed and intermittent connection. Also , the adsl link goes off after every 30min, resulting it to a total dis-connectivity. And this happen just after 6 pm all the official are turning deaf when try to explain the real fact and issues. Pls be careful of these official , and would suggest to take a proper action against them.