Same date; T2-G ILR due for Main Applicant; extension due for Dependent partner

[dogra]

Hi
Main applicant and dependent spouse both have visa expiring on 4th October 2017.
Main applicant is eligible for ILR(through 5 Years T2) but dependent partner has to get an extension. Dependent ILR is due in March 2020.
Main applicant has already booked an appointment for in person on 26th Sept 2017.

I am applying for PBS dependent online using the below link
visas-immigration.service.gov.uk/product/pbs-dependant-partner

As part of application when I try to pay for health surcharge the system is asking me to pay only GBP 100. But I know it should be GBP 600. I am sure I have made a mistake somewhere as I am trying to extend for another 3 years. Below is some main information I am putting in to the system
Your Details
Visa route --- Tier 2 PBS Dependant
Visa type --- Tier 2 (General); up to 3 years
You're joining or remaining with this person in the UK(Main Applicant)
Visa expiry date --- 04 October 2017(ILR application appointment is on 26th Sept)
Visa route --- Tier 2
Visa type --- Tier 2 (General); up to 3 years

Just as trial I put Main applicant visa expiry date as April 2020. Health surcharge then shows GBP 600.

My questions
1. Am I using the right application form?
2. Where else I can go to resolve this issue?

Thank for reading my rather long message. Any help would be highly appreciated

Regards

[dogra]

I called UKVI today. They told me that I can just add three years to current visa expiry date of Main applicant. i. e. 4 Oct 2017 and put 4 Oct 2020 in the online application. This way I would be paying right amount of Health Surcharge. They got a reference number for my call.
I thought I must update other people if they face similar problem.

[CR001]

She should apply alone and not put your details in.

User in link below paid the IHS separately on the IHS website and not as part of the online application process.

uk-tier-1-general-visas/pbs-dependant-e ... l#p1518541

[dogra]

She should apply alone and not put your details in.

User in link below paid the IHS separately on the IHS website and not as part of the online application process.

uk-tier-1-general-visas/pbs-dependant-e ... l#p1518541

From the solution proposed to me and from the link shared by CR001 it seems like UKVI don't mind as long as correct amount has been paid.

Thank you CR001 for your help.