IPv6 Prefix Delegation and terrible support

My setup is pretty simple

Comcast Gateway <-- --> Mikrotik Router <-- --> LAN

Since my comcast gateway is given a /56, I'm trying to assing a /64 to my Mikrotik so it can delegate addresses out to its hosts (there are no hosts directly connected to my comcast gateway). 

Unfortuantley trying to figure how to do something as simple as getting a /64 from a /56 seems to be an insane question! So far my my experianec has been :- 

1. Talk to Tier 1 told me they can't change my first part of my prefix that was set in stone (I tried to explain a little more what I was looking for) after what I thought was a "ah ha" moment, they escallated to tier two and promised a callback within 4 hours. 
2. Talked to Tier 1 again the next day... no call back, turns out the person didn't know the turnaround times properly and tier tow was already closed by th epoint they put the email in.
3. Email from Tier 2... issue resolved ... but what issue - they send me a note of my /56 address (ugh, not helpful).

Take two

1. Call tier 1 again, explain issue. 
2. Tier 1 apologizes and reaises the issue again to Tier 2 
3. No callback 
4. Call back tier 1, ask for complaints procedure was told " you just tell me" ok so what happens then... "I put it in your acocunt", do I get someone to talk to me about the complaint "not sure".
5. Speak to manager, manager assures me callback... no callback. 

Take three 

1. Call loyalty team, ask to cancel 
2. Explain problems with support, rep looks at notes and apologises, acknoledges failings, calls into Tier 2. Tier 2 can't help so escallates to Tier 3 - will have callback within 24 hours. 
3. No callback

Take four

1. Call in to tier 1 
2. Explain issue 
3. 25 minute hold - hung up on 

Take five 

1. Call in to tier 1 
2. Explain issue 
3. Person helpful this time, seems genuinly interested in helping, tries to get answers, not fully understanding problem but still super enthusiastic and trying their hardest. Even tries to track down a Tier 2 in the office to ask them. 
4. Told Its either a "cisco" issue, or a its not doable (while this may be true, It'd be great to get confirmation from Tier 2/3 who can tell me why its not doable or viable workaround). 
5. Told I will get a call back. 

So now need to wait again for a call back, I'm really not holding out much hope at this point so I am just posting here incase anyone else has had any luck with PD on DHCPv6 or any other way to get a /64 to their own router, or how they route their IPv6 ranges through to their own machines. 

Any help would be super apprechiated. 

Mitch