Help Constructing A Headache Query...

I have two tables, both with phone numbers and call times.

one is for incoming calls, one for outgoing calls.

I need to find all phone numbers from the incoming calls table where the number of calls exceeds 100 within the last 30 days, where the last call was within the last 15 mins, and where the number does Not exist in the outgoing call table within the last 30 days.

so far I have this...
(call record is the incoming, callout is the outgoin)

I believe this is giving me all records in the call record table that are within the last month, and not in the outgoing call table OR have not ben called within the last month..

SELECT cr.cli,min(cr.starttime)as "first call",max(cr.starttime)as "last call",count(cr.cli) as "number of calls"
FROM callrecord cr
LEFT JOIN callout co
ON cr.cli = co.cli
where (co.cli is null or datediff(dy,co.calltime,getdate())>30 )
and datediff(dy,cr.starttime,getdate())>30
group by cr.cli
order by cr.cli


i need to add in the 15 minute call check, and also only return those with a count of > 100

can anyone assist? i'm getting a headache :D

tia

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