The short answer is - you need to concatenate your two Fact tables into a single Concatenated Fact, and to name your timestamp field in the same way, and combine the two IntervalMatch relations into one. This will resolve your issues.
However, you will need to resolve other possible issues that come with concatenated facts - your two facts will not be linked anymore, when they are concatenated in a single table. The full answer to this question contains all QlikView data modelling techniques.
If you'd like to learn more about QlikView data modelling, I'd recommend my new book QlikView Your Business. In the book, I explain in a lot of detail how to work with multiple Fact tables and how to build Concatenated Facts properly.
We also teach advanced Data Modelling techniques at the Masters Summit for Qlik - coming soon to Milan, Italy!
Looks like you have 2 start / end timestamp pairs and have done 2 intervalmatch's. This will always end up with complications.
What I have done in scenarios like this is :
First process your Call Facts table and create a Facts table that has fields for :
start_call as [Fact Start] ,
end_call as [Fact End] ,
'Call' as [Fact Type] ,
...and your call dimension fields
Secondly process your Sales Facts and concatenate onto your Facts table with fields:
start_sales as [Fact Start] ,
end_sales as [Fact End] ,
'Sales' as [Fact Type] ,
...and your sales dimension fields
You will now have a single Facts table and can do a single IntervalMatch() on that against [Fact Start] and [Fact End]
In your front end objects, either have a List box to Select what [Fact Type] you wish to show, or use the [Fact Type] for Set Analysis in expressions.
This also adheres to the concept of having a single concatenated Fact table.