There is no minimum income requirement for the DTV, you do not need 2700 a month. You need 500K THB in a personal bank account. You can get a METV which is a 6 month visa but you can stay around 9 months if you time your extensions correctly.
TM30 is a requirement to report the stay of all foreigners. regardless of visa status. it still needs to be done. Yes, a few times a month is an acceptable cadence
Where did you apply? Send 6 months of bank statements with a final balance of 500K, highlight salary deposits Inc their slips. Send details of your work online, CV, website links, qualifications etc
KL is infamous for being the most demanding embassy to apply from and the requests you have posted show why. There are much more friendlier embassies near to KL to get the DTV so if you are not able to get the docs required for KL then apply elsewhere, Others have failed at one embassy and been successful elsewhere.