Verizon unwilling to to credit as promised

[Commodore64]

The internet was not functional in my home since July of 2019.  I have had numerous technicians to the home for the various issues.  The most recent technician suggested I get the G3100 Fios Router and extender.  This is $13 extra per month.  Verizon offered to credit me the $13 each month for the inconvenience to keep my monthly payment the same.   I have screenshots of everything including the $13 credit.   The customer service rep who made the promise advised that I would need to call in after setting up the new router and extender to request the credit and there would be copious notes memorializing same.  I said to the customer rep (and there is a screenshot of this) that "you are never going to give me the credit.  Verizon always does this and will screw me over."  Got everything set up on Saturday.  Guess what? Verizon is refusing to credit me. Finally spoke to a customer service supervisor who offered me 3 months (as they shipped the equipment in March) and 3 months going forward.  His reasoning was that "the screenshots don't say how long the credit was for."  Verizon has the worst customer service and they lie to customers all the time.  A "manager" is supposed to call me.  I'm sure that call will never be received.