Check and make sure that your Ooma Setup MAC address is set to Use Built-In. This is often helpful for dropped calls.
For dialing problem, for an Ooma Hub, the only prefix you can use is *99, although some people say that *82 helps also for the Hub.
Note: *99 can cause echo during the phone conversation.
Make sure that you have you have Enable 10-digit dialing at https://my.ooma.com/system
Don't rule out that your Modem isn't causing at least some of your problems. Find your Modem manual and do a Modem reset. Many Modems contain a battery which must be temporarily removed during the period of time that the Modem reset is being accomplished or the Modem reset will never be fully accomplished.
They/I can't hear me/them conversations is an individual problem that only Ooma can correct for you. You have to keep after Ooma Customer Support until they make corrections. I would talk to them, but only talk about the They/I can't hear me/them conversations as your problem. If you can get this part of your problems correct, it may correct other problems that you are having also.
Phone: 1-888-711-OOMA (6662)
Monday-Friday 7am-7pm PST
Saturday-Sunday 8am-5pm PST
When you can find some time:
Power off the Ooma device for 20 minutes. This allows time for the Ooma servers to reload/reset/correct your Ooma profile. Then repower the Ooma device and test.
Repeat this procedue up to there times in a row. That's why I said "when you can find some time".