Can i still get another COE from my previous company after a got one a year ago? I was planning on getting one this month because i can't seem to find it anywhere since it was a year ago is there any expiration to it?
This might also depend on your countrys law, but in most countrys the COE can only be demanded while you work or shortly after you leave the company. This is due to the circumstance that also other employments might change and no one might know what you did exactly. A mere confirmation can but often be achieved without further troubles.
My suggestion: Call the company and if possible the person you got your last COE from, surely this person still has a copy or might write you a new one. If you never got a COE or the old one is lost, tell them you will write the COE and send it to them, if they want to change anything you will frankly accept it and be happy about it. Stay positive and friendly throughtout the conversation! (If you do all the work they most likely will just sign the paper without changes and everybody is happy!)
Your certificate of employment (issued by the employer) should never expire as your employment during the relevant period is not something that will change over your lifetime.
Regarding the lost certificate, check with your former employer (I suggest emailing HR) and your declaration that you lost the original certificate should be enough for them to issue a duplicate. Since the matter on such certificates typically follows a template, it should not be a big deal for them and the new certificate for all purposes should be exactly identical to the previous one other than very few details like the issue date, the signature(s) and perhaps a note that this is a "duplicate" issued as per your request. If you happen to have a copy of the original certificate, that will make matters easy for everyone involved.
If the original certificate had some customized details which only you and your immediate team/boss knew about, that may pose a problem because you may not get an identical one especially if the current management is not aware of those details.