the whole unemployment insurance sign up and certification process is full of questions about retirement pensions. This is for a reason. There is lots of entanglement.
Each week that you have collected your unemployment insurance, you have filed a certification for it, filling out questions indicating that you had not worked that previous week, that you were able, available and actively seeking work, and there would probably be a few more certification questions. One of these would always be something about "have you begun collecting retirement benefits, has there been any change to a retirement benefit, pension, so on and so forth, anything you were drawing?" because yes, drawing a pension may make you ineligible for unemployment insurance. Certain kinds do, certain kinds do not. That is why as soon as you begun getting the pension you were supposed to report it, and the unemployment system would have gotten the necessary information and made a decision about whether you could legitimately collect both at the same time.
I gather you just didn't tell them. Right? Your bad. Because if this is a retirement pension which you report on your income taxes for the year, and based on your income tax forms, the system most definitely will cross match it with your unemployment and they very well may declare you overpaid when this happens. You can bet they'll eventually be in touch.
My best advice? Talk to someone within the state unemployment system. As soon as possible. Oh yes, you can get through and talk to a live person somewhere at some time. Keep trying. If you are going to be overpaid, the sooner you stop the checks and get this straightened out, the better off you will be, the less likely they will be to consider this fraud. And ultimately, they may not decide you are overpaid. But having this hanging over your head is not worth it, having them come back and demand you repay all your benefits a year or two after the fact is going to be rough on you. And they will eventually catch this.
Some kinds of retirement pensions, like social security retirement, are okay to be drawing and have no effect on your benefits as long as you do not remove yourself from the labor force. But other types of non-contributory retirement pension plans may definitely stop you from getting unemployment. Drawing out iras or 401k's in a lump sum is not the same thing as beginning to receive a regular monthly pension check, and does not affect your benefits. But in any case, they will need to make a decision, decide if you are overpaid, and then you and they can work together toward getting the money paid back if it is necessary.
Don't worry, if you simply cannot pay back an overpayment, and you have been fully cooperative with them about the situation, they will usually work with you as much as possible, may allow you to defer the payments, get a waiver, something. But stop drawing and start calling and asking and going about fixing this situation quickly.