When I flush the upstairs toilet the down stairs toilet bubbles and overflows for about 3 minutes, a few minutes later the toilet downstairs refills. PLEASE HELP

You have a main line clog, I sure hope you don't do laundry before you fix it.

Doug is right, stop flushing the upstairs toilet, using the tub or sink. They will all cause some form of backup or over flow until you get the main line opened. Actually the downstairs toilet will start backing up very soon tooo so locate your clean out and open it. Standing water means the plug is downstream towards the street, a dry clean out means the blockage is up stream back inside the house plumbing but after the toilet. Do not try to use chemicals like Draino or anything like that. Do not try to rod with some little 1/4" X 50' tape that you buy ay ACE. You need at least a 1/2" or larger rod, buy or rent at Home Depot or a store of your choosing.

Glad things worked out, now you can go do your laundry. Do have a question, did the city tell you why it needs yearly attention? That is not normal, did they find a break or low spot in the drain?

If the city is snaking out your drain then a plumber just got robbed of work. We consider that unfair competition and some plumbers sue the city over that.

Unless the city causes the problem, there is no way your tax money should go to fix it.