Client isn't paying

@dollorphanage this is main point ..... Why paid till 6 years but not for only 3 invoices ????

May be client understand that what is going on .....
Saying already that client paid for each invoice ..... means client is genuine ..... So why client is ignoring since 3 months only (I think 3 invoice in SEO will be monthly)
Reason of No reply .....
Generally for services client and company talk with each other by email ...... but he is not mentioning that what he received reason to decline all call or email.
Marketing Issue ......
Lots of minded marketing person doing his work from home ...... so may be some one convenience client that he is doing wrong and you should do this for best reason ....... and in few weeks he proofed what he said ........ then why client will reply????? ... if he know what is going on ..... if not this issue then he should clear points but as i think issue is like this.
There can be many other reason...
First and last point is client since 6 years ...... so i think client and service provider know very well that what is issue ...... we can suggest only.

According to me its normal condition in digital marketing ..... if you are winning always then should learn also for condition like this.