How long does it take to UPGRADE/FIX internet speed? I've been waiting for MORETHAN 3 MONTHS!

Does it really take MONTHS for AT&T to upgrade and fix internet problems?

I've called AT&T customer service many times and it seems we going in circles. 

Is my case (internet situation) really that difficult to solve?  Someone please enlighten me, sorry this is rather long but here it goes:

Our contract started December of 2016. We were not conscious of the internet speed then and  we went on vacation for 4 months starting February. When we came back we noticed our internet was slow and at times we don't have internet at all.  Our plan was Internet 12 but our max download speed was around 5mbps  which seldom happens, it is usually just 2 or 3 and upload speed was 0.6mbps or lower.

Our first call to AT&T was July 3, 2017 to complain about the slow speed. When we checked our account we noticed they don't have the Internet 12 plan anymore but Internet 25 with the SAME price. I asked the customer service if it is possible to upgrade it anyway they have the same price, she said yes - our appointment was set to July 5. An AT&T cable guy,  Andre, came the following day to check the cables outside the house in preparation for the upgrade. He said nothing was wrong and we'll have to wait for July 5 for the "internet guys" to check the modem and upgrade the speed. July 5 came and AT&T tech, Vince, checked our connection and told us that he cannot upgrade the speed because we only have 1 cable and it has to be 2.  Based from his explanation, to have an internet speed of 25 there should be 2 cables going to our house, but when he checked it we only have 1. He said the "cable guy" who checked it previously should've known that and did something.  He set another appointment for the cable guys to fix it but when they came  on July 7 they said they couldn't do anything because the problem is in the cable UNDERGROUND, so they need to dig and another group of people is incharge of the digging. 

From July 3 until this afternoon October 23, I already made 14 phone calls to AT&T. They dug our front yard including our neighbor's front yard 3x! They seem to always have the WRONG SPOT and could not find the missing cable or whatever they are looking for. The interval of each digging is almost one month because they have to wait for other people like PG&E to check or clear the area. Whenever I chanced upon the cable guys they'd always tell me they could not do anything until they find the right spot so they have to wait for the diggers to finish their job, and the internet techs on their part would say they also can't do anything until the cable guys finish theirs. 

Right now, there is still a BIG HOLE in our front yard and I do not know the status of our upgrade.  Our internet is still ON and OFF and our download speed is in its lowest at 0.61  while our upload speed is 0.9 -- it got worse! When I called AT&T last week they said they can't give a status but instead  asked me to call Burywire company which I did, but even them can't give me anything. AT&T said they'll call be back to inform me of the current status but they never called - they did this to me in 2 separate occasions already. 

It is frustrating, how long should we wait? I'm certain this connection problem has been going on since the initial installation, it just went unnoticed because we went on vacation for months. The customer service always promise to do this and that to expedite it but they can only rely on the "orders" written in their computer nothing more,  but it has been morethan 3 months now. WHAT SHOULD I DO?