Access tin.nsdl.com and register yourself for online view of form 26AS.
However, the best course of action is to get your ex-employer to revise his TDS return and get your PAN number entered correctly. At least get into some form of reconcilatory approach. After all, solutions to most problems are found if resolved mutually and amicably between two parties. Whoever is handling your ex employers TDS can get the PAN number rectified.
Now this is something that can be done. You only have to get the person who is authorised to do it to do it. Throw aside the ego and talk if that is the issue. If both parties are cool, there is solution. You would need to be very cool rather than agitated and you can get the matter resolved very soon as over sometime the other side too will cool.
Remember, you have everything to loose.
My case was a little different. I do not look after TDS at my employers but the accountant we employed was too incompetent and he deposited all my salary TDS under 194C while he was on the job. The previous accountant before him had paid correctly u/s 192 but did not quote PAN properly. So when we booted out the incompetent accountant (they are just under qualified data entry operators) I had to take charge of TDS and get the matter rectified. Because of the wrong payment of section 194 C, we had to ask for adjustment of amount to another a/c where short deduction was done on that account and had to again pay under 192 with interest. For the returns where PAN was wrongly quoted, we had to revise the quarterly return with the correct PAN Number and regenerate the acknowledgement.
Therefore everything is possible to do. You have to get the authorised person to do it. Also get your PAN number corrected on the TDS certificate as that can be presented to ITO.