I cannot add payment to my apple id and cannot upgrade my icloud storage...the subscription was running earlier but stopped

You can have a credit card / debit card on file and an Apple Account balance.

If you have set your Apple Account balance as your default payment method, your default payment method will be used first by Apple when you need to make a payment.

Some purchases might require you to have a credit card on file, even if you use your Apple Account balance to make the purchase.

See the following Apple articles:

Add a payment method to your Apple ID -> Add a payment method to your Apple ID – Apple Support (UK)

Remove a payment method from your Apple ID

Remove a payment method from your Apple ID - Apple Support

⤵️

If you can't remove a payment method

If you have subscriptions like iCloud+, have an unpaid balance, or you use purchase sharing, you must keep at least one payment method on file.

• Do you have a subscription? You can cancel iCloud+ and cancel other subscriptions from Apple. When your subscription period is over, remove your payment method.
• If you're in a Family Sharing group and you use purchase sharing, the family organizer must have a payment method on file. If you're the family organizer, turn off purchase sharing, then remove the payment method.
• If you have an unpaid balance, you might not be able to remove a payment method. Instead, change your payment method.
• If you still can't remove a payment method, contact Apple Support.

What you can buy with your Apple Gift Card or Apple Account balance

What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)

• Some purchases might require you to have a credit card on file, even if you use your Apple Account balance to make the purchase.

and cannot upgrade my icloud storage...the subscription was running earlier but stopped

When did you downgrade your iCloud subscription?

The iCloud + subscription will be terminated depending on the start date.

If you start on August 1 and are going to cancel now, the subscription will stop on November 1, a monthly term is used.

Perhaps you have to wait, then try again to upgrade then iCloud storage.

See this Apple article: Upgrade to iCloud+ -> Upgrade to iCloud+ - Apple Support

If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK)