hmmm should i say night mare?

i had my main domain hosted on my servers and my subdomain pointed to their name servers, it was working fine for a bit and then suddenly one day it stopped. Since then it has been 5 days and they keep arguing that main domain and subdomains have to be hosted or pointed to same name servers. I know for sure it doesn't have to be that way as i have subdomains with other resellers. Website is live and my billign software (WHMCS) is installed on the subdomain but now its not working!!! driving me crazy!

Added to this...they change ip address on the account with no notice...so all the licenses either they give free or i installed stopped working, websites were always down!

i am a reseller there and i am running out of patience...their support is stupid or am i just stupid not able to understand/fix the subdomain issues!