1. Is it mandatory to fill estimated Return if the company transaction comes under D-02?

2. Can we fill D-02 for transaction below 30lakhs if we have advance tax to claim?

3. What to fill D-02 or D-01 if my sales is 28 lakhs and purchase is 49lakhs?

4. How to tackle with the mismatch if purchase is over 30lakhs but sales is only 20 lakhs ?

#1. Filing Estimated Tax Return and making payment of installment tax is exempt only if following conditions are met:

a. Business Filing D01 Return

b. Total tax liability is less than 7500 

So, business filing D02 return should compulsorily file estimated return.

#2. Requirement to file D02 return is to have annual turnover exceeding Rs. 30 lakhs. If you try filing D02 return you can see initial tax rate is automatically computed for 30 lakhs and blank text box is available to enter the exceeding turnover amount, so D01 return is filed for turnover less than 30 lakhs.

If tax paid is higher than tax liability, taxpayer is allowed to apply for refund of the excess tax paid within 2 years of payment made or end of fiscal year. Income Tax Authority shall refund the excess tax paid or settle with the tax liability unpaid till date. So file D01 return and proceed for tax refund.
Note: It is better to visit your IRO to know more about the tax refund process.

#3. Requirement to file D02 return is to have annual turnover exceeding Rs. 30 lakhs. If you try filing D02 return you can see initial tax rate is automatically computed for 30 lakhs and blank text box is available to enter the exceeding turnover amount, so D01 return is filed for turnover less than 30 lakhs.

#4. Please elaborate your problem here, we could not understand what is the mismatch here.

Purchase may be over the sales value but calculation of profit is --> Sales - Cost of Sales (not Purchase).

For annual turnover less than 30 lakhs, please file D01 return.

my turnover is around 9900k and i am filing D2  after filing all the relevent column a popup occurs with a message of you turn over should be greter than 300k ...

Retry in other browser, else retry using new submission number. this seems to be technical error.